The images in the text are from digitized works cited and created from pages downloaded from the BHL. The photos of Agabus nebulosus are by Niels Sloth (with permission).

Rhantus
There have been quite a few changes in the species names of the European Rhantus species. It already started with the genus name. which is a transposition of the (ancient) Greek ραντος - rantos, for which, because of the breath sound that follows the r, rhantus is the correct transposition, but was first published as Rantus by Dejean. The meaning of the Greek word could mean something like: 'moisten' (Brink, P. in ICZN 1954, see Literature). The meaning of the species names is shown on the previous page.

Colymbetes pulverosus Stephens, 1828) was finally designated as the type species in 1954, but the species itself was given the name Rhantus suturalis (Macleay 1825). In Nilsson's catalog (2015, update Hájek 2022), a large number of species names can be found. Balke et al. (1993) provide a thorough revision of the types, the article by Bousquet & Bouchard (2012) provides clarification in the confusing piece of the history Dejean (1833), but Balfour‑Browne in ICZN 1954 in particular is leading.

Johann Forster
In 1771, this German researcher with Scottish roots published his "Novae species insectorum". On page 56 he described (in Latin) a water predatory beetle, which he called Dytiscus nebulosus. "ELYTRA livida, punctis minimis nigris nebulosa" elytra with small black dots like a nebula. That is reminiscent of the Rhantus beetles, but this beetle belonged to a different group, it was later moved to theAgabus group and is now called Agabus nebulosus (Forster, 1771). We will encounter this beetle again at Johann Bergsträsser

On page 57 (see image above) Forster described a beetle that does belong to the later Rhantus genus, and called it Dytiscus exsoletus, which makes this name the oldest for that species, and thus it is now called Rhantus exsoletus (Forster, 1771).

Johann Bergsträsser
This German teacher had beautiful books published on the insects of Hanau and the surrounding area, enriched with clear color plates (copper engravings) in 1778 and 1779. The first volume (1778) begins with the "der Schwimmiäger oder der Gelbsaum". the yellow-edged water beetle and, in addition to land beetles, a number of water beetles are also described.

As one of those beetles, on page 30 we find the "𝔇𝔢𝔯 𝔤𝔢𝔷𝔢𝔦𝔠𝔥𝔫𝔢t𝔢 𝔚𝔞ſſ𝔢𝔯𝔨𝔞𝔣𝔢𝔯", Der gezeichnete Wasserkäfer)¹. The image, figure 10 on the adjacent page, shows a beetle with greenish elytra and a yellow pronotum with four black points.
On page 31 the Latin name is presented: Dytiscus notatus, the 'marked diver'. However: later researchers have agreed that this was a beetle of the same species as Dytiscus nebulosus, which, as described above, was already named by Johann Forster in 1771, an older and therefore valid name. The notatus name was therefore, but much later, declared invalid and would leave a long trail of confusion...

On the left a photo of Agabus nebulosus (copyright Niels Sloth, with thanks for his permission), reduced to approximately the same scale. With some difficulty the four dark points on the pronotum can be recognized. But the image deviates quite a bit from the drawing. And then the beetle in this photo may well be a specimen, where the points look a bit like those on the old, colored copper engraving image. Often they are merged into two dumbbell-shaped spots, or the outer two are barely visible.

It is difficult to recognize a beetle from a description and a drawing. I also don't think many of the beetle drawings in later field guides look very similar. Determination of a photo is also not always possible. Because the earlier entomologists could not always view each other's collections, the errors occurred.

On page 42, "𝔇𝔦𝔢 ℨ𝔴𝔢𝔦ſ𝔱𝔯𝔢𝔦𝔣𝔢" is presented, "Die Zweistreife". Bergsträsser wrote that despite all kinds of comparisons he could not decide whether that beetle was already known to naturalists. That is why he described it in a bit more detail, "zumal da unsre Abbildung das Unterscheidende auf den Flügeldecken nicht ausgedruckt hat". And that was true, see the image on the left. He described this distinction as: 1) two dotted lines, running parallel lengthwise, 2) that they both had a pale yellow seam, both along the inner and outer edges, with that along the outer edge becoming noticeably wider towards the back, but that along the seam was narrow. He named the beetle Dytiscus bistriatus.

Much later it was discovered that Bergsträsser's "Zweistreife" was a (rare) Rhantus species. The name he came up with is the oldest known, so the beetle is now called Rhantus bistriatus (Bergsträsser, 1778).

The second volume (1779) of his book is about butterflies, a few Maculinea species have been named by Bergsträsser.

Johann Fabricius
This Danish entomologist was a student of Linnaeus and he described about 10,000 species. His collections were divided between Copenhagen and Kiel. After WW2, the Kiel section went to Copenhagen, in 2017 everything went to Kiel (see the link at Fabricius at the bottom of the page). He published a Systema entomologiae in 1775 , perhaps inspired by his Systema naturae . But in another work, the Species insectorum... Tomus 1 (= Volume 1) from 1781, page 296 contains an important link in this history.

There he described a dark Dytiscus beetle, having a yellow pronotum with four black points. He identified it as: Bergsträsser's Dytiscus notatus. But later specialists assume that this identification was wrong: the beetle of Fabricius was not the same species as Dytiscus notatus of Bergsträsser, the later Agabus nebulosus ! The species that Fabricius named Dytiscus notatus was the later Rhantus frontalis, as we shall see.

Above is a photo of Agabus nebulosus (left) next to Rhantus frontalis. Fabricius described four black dots, but how he saw them on the pronotum of R. frontalis is somewhat mysterious. Those 'four dots' of the left photo are just a way of looking at it, the outer two can also be interpreted as part of the 'shallow W ' that, just like in R. frontalis, runs along the rear edge of the pronotum. The two inner dots can also be fused, as in the specimen in the photo by Jirí Hájek in Foster&Friday (2011, 130 Plate 50). Then the picture looks even more like that of R. frontalis. Fabricius's mistake is understandable, especially in his time.

Several entomologists studied his specimen(s?) of this species and the "Dytiscus notatus Fabr." has probably been given a solid status. If only he had not identified the beetle as Bergsträsser's and given it its own new name, the confusion would have been a lot less. You could even say that Fabricius' notatus became valid, when Bergsträsser's was cancelled due to his incorrect determination, but that is not how it went.

Three more names from Fabricius' work need to be excavated for this history. First Dytiscus haemorrhoidales from "Mantissa insectorum" (Fabricius 1787) and Dytiscus agilis from "Entomologia systematica" (Fabricius 1792). These names were later made synonymous (Nilsson, 2023), the oldest is D. haemorrhoidales and therefore the valid name. The beetle was not a Rhantus species, but was later named Copelatus haemorrhoidales and today it is called Liopterus haemorrhoidales (Fabricius, 1787).

The last name is Dytiscus adspersus from "Systema Eulatheratorum" (Fabricius, 1801). This beetle later turned out to be Rhantus bistriatus.

Étienne Geoffroy: punctatus
An old synonym for Rhantus suturalis is Rhantus punctatus (Geoffroy, 1785). This name was suggested by the French pharmacist and entomologist Geoffroy as Dytiscus punctatus. This on page 70 of a book about the insects of Paris and the surrounding area. He wrote this together with the French statesman, chemist and entomologist Antoine de Fourcroy (1785). But the punctatus name was not valid, it was occupied (a homonym), because Scopoli had already introduced that name for Dytiscus sulcatus in 1763 (Nilsson, 2015, Scopoli 1763). Strangely enough, Scopoli also included Linnaeus's older sulcatus name. Scopoli's name was ultimately not accepted either, and is a younger synonym, that beetle was eventually called Acilius sulcatus (Linnaeus 1758). See also the »page about scientific names«. You would think that this would make the puncatus name available again and that it would be the oldest, so you will encounter it in various publications, also known as Rhantus punctatus (Fourcroy, 1785). There have of course been many beetles that were given the punctatus designation, Rhantus frontalis for example, which was once also described as Dytiscus punctatus Hoppe, 1795 according to Nilsson, (2015).

Joseph de Clairville: Colymbetes
his Swiss botanist and entomologist, wrote the "Helvetische Entomologie" in Zürich in 1798, in which he proposed a new classification method, with the aim of making a sound identification possible. He himself mentioned the analogy of his system, based on the "Fühler und die Fuſsglieder", maybe inspired by the stamen-based plant system of Linnaeus. Fabricius, who surprised him with a visit, encouraged him and even helped spread the word. In the second part, published in 1802, new genera were introduced, among others, Noterus and Colymbetes, with the species Colymbetes striatus, Colymbetes fuscus, but on the previous pages, strangely enough, he also proposed as Colymbetes species Dytiscus Roeselii Fabricius 1792, which now called Cybister lateralimarginalis. A list of "Druckfehler" (Errata) is included at the front of the book, which includes an additional paragraph with 14 Colymbetes species, species from the Dytiscus genus. But they now have other genus names. No future Rhantus species can be found in that list. However, later researchers classified some of their found beetles into the Colymbetes genus - and later a new group, the Colymbetini, was founded by Wilhelm Erichson, see further below. So some of that layout of the Clairville has survived.

Leonard Gyllenhal
This Swedish military officer and entomologist published a number of (Latin) books about beetles in Sweden in 1808. In the first volume, Dytiscus conspersus is listed on page 482. This is accompanied by the addition "Marſh. ent. br. 427. 37. Schönh.ſynon. 2. 22. 66. ", which means that he interpreted the beetle(s) as Dytiscus conspersus, Marsham. But unfortunately that was also a mistake, Marsham's beetle was an Agabus species and is now called Agabus conspersus (Marsham, 1802). Gyllenhal's Dytiscus conspersus later turned out to be the species R. suturalis. (Balfour‑Browne in ICZN 1954).
On page 483, Dytiscus notatus is on the list, he lists it as that of Fabricius, again the beetle incorrectly identified by Fabricius. Later Dejean incorrectly interpreted this name as belonging to Gyllenhal himself. The beetles themselves appear from the description to have indeed been R. frontalis, the same as those of Fabricius.
On page 485, as no. 19: D. collaris, as being from Paykull. The oldest name for this beetle, Forster's: Dytiscus exsoletus is not listed, but it was that species, as has been determined.

Dytiscus grapii is listed as a valid name on page 505 , with the addition "Habitat in aquis Laponniæ Dom. Grape". This name is now, because the Nartus subgenus of Rhantus Zaitzev, 1907, has been rehabilitated to a genus (Balke et al., 2017), Nartus grapii (Gyllenhal, 1808).

MacLeay and Stephens
In 1825, world traveler and entomologist William MacLeay (son of Alexander MacLeay) gave a beetle species found in Java the name Colymbetes suturalis, thus placing it in the genus Colymbetes.

In 1828, the English zoologist Stephens named a beetle species found in England Colymbetes pulverosus Knoch, with an image shown on the left. However, Knoch never published that name, so the name belongs to Stephens himself, see also further in this story.

Later Balfour-Browne (1939) showed that these species were the same. MacLeay's name is older. That is why the name has now become: Rhantus suturalis (MacLeay, 1825)).

Thaddeus Harris
Was one of the American entomologists. He wrote an article about insects (especially their harmful effects) in a magazine for farmers in New England. In 1828 he described the capture of nine beetles, of a species he calls Colymbetes suturellus, "Extremely like c. collaris, Gyllenhall...", but then "..much darker beneath, paler above.." The species name collaris was, as we read in Gyllenhal, not by that author himself, but by Paykull. Moreover, that was a different species, namely R. exsoletus. Harris's name for the species he described is the oldest, eventually becoming Rhantus suturellus (Harris, 1828).

Dejean and Eschscholtz: Rantus
A few years later, the Baltic-German physician and natural researcher Johann von Eschscholtz visited the French general and entomologist Auguste Dejean to compare his collection with his own. (Wikipedia). The gentlemen classified many of the beetles together, sometimes under new names, which were later published by Dejean (Dejean 1833).

In his 'second catalogue' a classification for the "HYDROCANTHARES" is proposed from page 53, with the future Rhantus group on page 54 , but under "Rantus Eschscholtz", without the h and Eschsholtz as inventor. That wasn't a bad idea, but unfortunately the synonymization went a bit wrong. He included eight beetles under that group, see image below (including synonyms, there are 14 names). He did not name a type species. The groups with a curly brace in front are important here, which will now be discussed one by one. Anyone who loses the thread here is in good company: the ICZN at one point considered annulment of Dejean's Catalogue for the classification.

The first name he proposes is He proposes Rantus suturalis Dejean, as a new name for the Dytiscus notatus of Gyllenhal. Perhaps he wanted to indicate that this should be the typical species. But Gyllenhal, as already described in the paragraph about him, did not record this as his own new name, but as the Dytiscus notatus of Fabricius! So the species name was invalid.

As the next species, Dejean proposes Rantus notatus Fabricius, 1781, as a new name for that same(!) D. notatus, and also for the synonymous D. conspersus Gyllenhal and Colymbetes pulverosus Knoch. The latter is, as stated, Colymbetes pulverosus Stephens, 1828, the same species as D. conspersus Gyllenhal, 1808 and the two together ultimately the same species as Colymbetes suturalis MacLeay, 1825. (Balfour‑Browne in ICZN 1954). But the D. notatus of Fabricius is of course not a synonym here, it is the other species, which is now called R. frontalis!

The next species: Dytiscus "Agilis.Fabr.", was not a Rhantus species, as previously stated by Fabricius. Harris' suturalis should be suturellus. So finally the intended species here is: Rhantus suturellus (Harris, 1828).

Rhantus adspersus has, after years, been replaced by R. bistriatus (Bergsträsser, 1778), the 'Zweistreife', see above. The species D. collaris (name of Paykull, see Gyllenhal) and insolutus turned out to be exsoletus, i.e. a different species. This has caused a lot of confusion: in England the name R. bistriatus stood for the species that was usually known in Europe as R. suturellus (van Nieukerken, 1992). In Foster&Friday (2011) the adjustment to the European situation is mentioned. See also further, under Gemminger and von Harold.

Wilhelm Erichson
In 1837 the German entomologist Wilhelm Erichson wrote a book about the insects of Berlin and the surrounding area. In it he provided a structured classification, which already shows the basis of the current system as far as water beetles are concerned. It was made possible for him to study, among other things, the beetle collections of Fabricius in Copenhagen and Kiel. This also allowed Erichson to bring some clarity to the cloudy naming. For those who want to read it, here is a more detailed description of its layout on a »separate page«. In short, the new group he founded is important, the Colymbetini, including Colymbetes fuscus and Colymbetes paykulli Erichson, 1837 (which he, as the author name shows, gave the oldest name), and the current Rhantus beetles.

His description of Rhantus suturalis (still known as Colymbetus pulverosus) is apt. He also wrote about that species, very enlighteningly: "Count Dejean considers this species to be the D. notatus of Fabricius, but I have convinced myself in the Fabricius collection that the usual identification is the correct one." (loosely translated). So: Dejean was mistaken, Colymbetes notatus is the Dytiscus notatus of Fabricius, the current Rhantus frontalis.

Frederick William Hope
The clergyman and entomologist FW Hope pointed out various type species in his 2nd "Coleopterists manual" of 1837, see the image below.

For Rantus he chose Dytiscus pulverosus Knoch. But August Knoch never published the name Dytiscus pulverosus. Hope almost certainly meant the species Colymbetes pulverosus Stephens 1825, because Stephens himself also synonymized it with Knoch's name, in his work of 1828 (Balfour‑Browne, J., in ICZN 1954).

Louis Agassiz: Rantus to Rhantus
In 1846, the Swiss scientist Louis Agassiz pointed out the incorrect translation of the Greek name into Latin, after the r had to be h, which represents a breath sound, as described above. Not everyone thought that was a good idea. But the new name Rhantus was widely adopted.

Gemminger and von Harold - aberratus
These two German entomologists published an extensive beetle work in several volumes. In volume 2, from page 448, a list of Rhantus synonyms, parts of which are below. We see that Rhantus aberratus is given, as their own new (Nobis) name, for the Rhantus adspersus of Fabricius.

And it gets worse, because they synonymize Bergsträsser's Rhantus bistriatus with Harris's Rhantus suturellus. This may have been the reason why English entomologists knew a different bistriatus than their European colleagues for a long time.

It is correct that they synonymize suturellus with the suturalis of Harris as in Dejean's Catalogue, because the name was given incorrectly there, as has already been said in the Dejean section. The invalid name agilis, which was used for several Rhantus species, is not considered here.

John Balfour-Browne and the ICZN, Opinion 289
There was confusion surrounding the Rhantus group, especially about the type of species and the spelling of the name. The English entomologist Francis Balfour‑Browne wanted to reverse the name change to Rhantus in 1935 at the ICZN, because, he felt, according to the rules there was more justification for the original name, misspelled or not. Francis' son John Balfour‑Browne wanted to do something about the confusion. From 1940 onwards he developed well-founded proposals to the ICZN, which, after delays (WW2) and an extensive treatise, ultimately led to the publication of "Opinion 289" (ICZN 1954) with the decisions in 1954. These were: acceptance of the genus name Rhantus Dejean 1833 (despite protests from, among others, his father) and acceptance of the type species proposed by Hope in 1837, i.e. Colymbetes pulverosis Stephens 1828. And finally, because John Balfour‑Browne argued that in 1939 had already shown that Colymbetes suturalis MacLeay 1825 is the same species, suturalis should be included as a species name ("trivial name", as a species name has been referred to since 1953, according to Hemming (in ICZN 1954), that instead of the "specific name" ).

Michael Balke et al.
Unfortunately, this did not really settle the matter. The various synonyms persisted, possibly also due to the enormous number of species found worldwide. Ultimately, the decision was made only in 1993, when R. suturalis was chosen as the name for a group of beetles that share at least one anatomical characteristic.)² Colymbetes suturalis Macleay, 1825 was designated as the so-called Lectotype.

THE END ?
Is that the end of it? Certainly not, the Rhantus genus is still in full swing. For example, two new genera were proposed in 2017: Meri‑diorhantus and Caperanthus. Species were moved to the genus Carabdytis Balke (Balke, 2017). This is based on molecular phylogenetic analysis. And it won't be the last...

---

Footnotes:

)¹ The Fraktur 𝔞 umlaut is not available in Unicode.

)² In this case the presence of suctionhairs on the parameres.