Digitized works cited are pages downloaded from the BHL.

Erichson had completed his studies in medicine and surgery in 1832, but his dissertation Genera Dyticeorum seems to be a sign of his real passion: insects. In 1837 his "Die Käfer der Mark Brandenburg" was published. It is a clearly structured work of more than 700 pages with a classification that, as far as water beetles are concerned, is already very similar to that of our time. He wrote that his classification corresponded to "der latreille'schen". For this work he visited Copenhagen and Kiel, among others, to view the collections of Fabricius, as well as those of Knoch, which yielded many valuable notes. Although he, like many entomologists, disapproved of introducing genera in a "lightly superficial manner", he himself introduced the Colymbetini as a new group.

The book begins, as "Erste Familie. Caraben." - the ground beetles. From page 140 onwards come the water beetles: "Zweite Familie. Dytiscen ." See also the chart below, which I have completed up to the fifth family. The rove beetles (Staphylinidae) fill most of the rest of the book. About the Dytiscus family: he wrote that he was going to use Linnaeus' name Dytiscus again, instead of the Dyticus in his earlier work. This is because the -iscus appendage can be seen as a diminution and "auf jeden Fall hat Linné den Namen zu oft braucht, um annehmen zu könnem er sei durch irgend ein Versehen" Dytiscen " enstsellt." Also see this »page on the Dytiscidae«.

A number of the current genus names were not yet available, for example the current Graphoderus species are still listed here under Hydaticus. The Rantus genus has also not yet been included, although those species are already included in the Colymbetes genus.

That genus starts in the book with "C. Paykulli" as first species, for which synonyms are given, among others: "Dyt. striatus Payk. Faun. Suec. I. 202. 11. - Gyll. Insc. Suec. I. 476. 10.", but Erichson wrote that he learned from "Herrn Westwood" that these synonyms are incorrect. Because that beetle, described by Linnaeus as D. striatus and is also present under the name D. striatus in the collection of Fabricius, is in fact "Dyt. Bogemanni Gyll.", which Erichson describes as the next species, number 2. This makes the name published by Erichson for this first beetle the oldest. The current name is Colymbetes paykulli Erichson, 1837. Beetle 2 is now called Colymbetes striatus (Linnaeus, 1758), which does not occur in the UK or the Netherlands. Colymbetes number 3 is the common C. fuscus (Linnaeus, 1758).

Then the current Rhantus species follow. Colymbetes number 4 is the current Rhantus suturalis, which Erichson aptly describes. Because an image of the digitized page would be unwieldy, the text is shown here (with some omissions). This has the advantage that you can use Google translate, or an alternative on the text.

4. C.pulverosus: (followed by a Latin description) - Long. 5½ lin.
Sturm Deutschl. Ins. VIII. 78. 4. t. 194.
Dyt. conspersus Gyll. Ins. Suec. I. 482. 16.
Rantus notatus Boisd. et Lacord. Faun. Ent. Paris. I. 311. 2.
Länglich eiförmig, ziemlich flach gedrückt. Die Oberseite ist gelb. Der Scheitel und zwei mondförmige Flecke zwischen den Augen sind schwarz. Das kurze Halsschild hat in de Mitte einen kleinen schwarzen Querfleck. Die Fügeldecken erscheinen durch die dichten, oft zusammenfliessenden schwarzen Puncte, die sie bedecken, und die nur den Aussenrand und eine feine Linie neben der Nath freilassen, braun. Die Unterseite des Körpers, auch die des Halsschildes, ist schwarz: die Beine sind röthlich-gelb.
     Ziemlich selten.
     Marsham's Dyt.conspersus ist eine Abänderung des Agab.bipunctatus. Graf Dejean hält (Catal. p. 54) diese Art für den Fabricischen D.notatus, ich habe mich aber in der Fabricischen Sammlung überzeugt, dass die gewöhnliche Bestimmung die richtige sei.

With this monograph, Erichson clears some cobwebs from the naming of this beetle, the line about Dejean's mistake being especially illuminating. The next beetle is Rhantus frontalis , which looks very similar to this species:

5. C.notatus: ((following Latin description) - Long. 5 lin.
Sturm Deutschl. Ins. VIII. 75. 3.
Dyt. notatus Fabr. Syst. El. I. 267. 50. - Duft. Faun. Austr. I. 263. 19. - Gyll. Ins. Suec. I. 483. 17. Schönh. Syn. I. 22. 67.
Rantus suturalis Boisd. et Lacord. Faun. Ent. Paris. I. 311. 3.
Länglich eiförmig, mässig gewölbt. Der Kopf gelb, Stirn und Scheitel schwarz, mit einem paar gelber Puncte bezecichnet. Das Halsschild ist gelb, die Mitte des Hinterrandes, einen grossen Querfleck in der Mitte und oft auch ein Punct zur jeder Seite schwarz. Die Fügeldecken sind wie beim vorigen gefärbt: die beiden Reihen eingestochener Puncte, die den verwandten Arten zukommen, fehlen. Die Unterseite des Körpers ist schwarz, die des Halsschildes end der gemeinschaftliche Kiel der Hinterhüften gelb. Der Hinterleib ist beim Männchen schwarz, die Ränder der Segmente gelb: beim Weibchen gelb, an den Seiten schwarz gefleckt.
     Beim Weibchen sind die Flügeldecken bald ganz glatt, bald in grösserer oder geringer Ausdehnung und Stärke mit eingeritzten Strichen bedeckt..
     Sehr häufig: im Winter unter feuchtem Moos.

Another accurate description. Note the synonyms for this beetle in the Faune Entomologique by Boisduval & Lacordaire: they are 'exactly the wrong way around' for both species, perhaps these authors followed Dejean.

Colymbetes number 6, C. infuscatus, is given in Nilsson (2022) as a syntype for the C. notaticollis of Aubé, indeed this synonymization can be found in Aubé (1838), with a reference to Aubé (1836), which also contains an image that can be found. The name coined by Aubé is older, the beetle is now called Rhantus notaticollis (Aubé, 1838). This species does not occur in the UK or the Netherlands.

Colymbetes nummer 7, C. bistriatus is the Dytiscus bistriatus of Bergsträsser, the current Rhantus bistriatus (Bergsträsser, 1778).

Colymbetes number 8, C. collaris is the current Rhantus exsoletus (Forster, 1771). Erichson wrote that as many males with short claws, comparable to those of the female specimens, were found as males, "solche, bei denen sie von bedeutener Länge, und nachdem sie gleich an der Wurzel gebogen sind, fast gerade auslaufen." The latter description fits with exsoletus. Perhaps there were specimens of R. latitans, which look a lot like exsoletus, but the males have short claws (van Nieukerken, 1992). Erichson thought it too far fetched to consider them as a separate species. A further complication in the monograph on this beetle is the listing of Dytiscus adspersus Panzer as a synonym, even though it has now indeed also become R. exsoletus. Because there is also an adspersus of Fabricius, see the next beetle, below.

Colymbetes number 9, Colymbetes adspersus is a tricky one. According to the description it seems it could be Rhantus suturellus. Erichson gives as a synonym Dytiscus adspersus of Fabricius. But that is the beetle that, according to Nilsson (2022), is now called Rhantus bistriatus. The issue became even more complicated when the adspersus of Fabricius was described by Gemminger and von Harold as Rhantus aberratus (source: GBIF.org). See the previous page.

Colymbetes number 10, Colymbetes grapii, on the other hand, is simple: as described on the previous page, this became Rhantus grapii and later ended up in its own genus as Nartus grapii, see also the previous page.

After this series of Colymbetes species, Erichson continues with the Ilybius genus, which he also introduced. We will not consider the rest of his accurate descriptions of the water beetles here.