Dytiscus unistriatus Schrank, 1781 : 205

Fery, Hans, 2019, Nomenclatural notes on some taxa of Bidessus Sharp and designation of a neotype (Coleoptera: Dytiscidae: Hydroporinae: Bidessini), Zootaxa 4565 (4), pp. 579-589 : 583-584

Dytiscus unistriatus Schrank, 1781: 205

The text in Schrank's work is reproduced in Fig. 5.

Schrank refers also to Geoffroy (1762), but he gives an additional rather detailed description and an exact type locality—a water cistern in the botanical garden in Vienna ( Austria): " Habitat Viennae in aquis stagnantibus, in conservis cisternarum Horti botanici." Notes: In the time span 1762–1773 Schrank passed several small periods of his life in Vienna. In 1809 he became the first director of the newly founded botanical garden in Munich (see Stolberg-Wernigerode 2007: 518–519).

The meaning of " Einstreifigter Wasserkäfer " is " water beetle with one stria ". The translation of the Latin description is: " Barely the size of a water flea. I possess a single specimen in my collection, which when it could be included in it [the collection], it was glued onto a little piece of paper, hence I don't know which colour it had on the underside, since I could not examine it alive. Black head, saturated dark pronotum, behind its centre with two slightly curved engraved lines, which are continued on the base of the elytra. Otherwise no punctures or grooves, apart from the only one near the inner margin of each elytron, which is simple, and not dotted. The colour of the elytra is less dark than that of the pronotum; with base, exterior margin and apex yellow." I am not fully sure about the translation of a part of the last but one sentence (underlined), but later Schrank (1798: 719) gave a description in German which is very similar to the Latin text above and contains the sentence (translation by me): " On each elytron a single, impunctate, engraved stria, near the suture."

The identity of Schrank's taxon is unclear because Schrank's description—although comparably detaileddoes not allow a reliably identification of his taxon. The name is—like those of Geoffroy, O.F. Müller and Goeze— a nomen dubium. It is likely that Schrank's single specimen from Vienna is what currently is treated as Bidessus unistriatus , but according to the description it may have been also a specimen of Hydroglyphus geminus , B. grossepunctatus , B. nasutus Sharp, 1887 , or B. minutissimus . On the other hand, I have studied 12 specimens from the landscape "Lobau" which is situated ca. 8 km east of the Vienna botanical garden. These specimens agree fully with what is currently understood under B. unistriatus Goeze. Because Schrank refers also to Geoffroy (1762), the syntype series encompasses not only the specimen from Vienna, but also the specimens which Geoffroy has studied (Article 72.4.1 of the ICZN 1999). Hence the type locality is " Vienna and Paris environs".

Evenhuis (1997: 705) gives for Schrank's collection: "Whereabouts or existence of any personal insect collection is unknown." My requests at several institutions were unsuccessful (MNB, NMW, SDEI, ZSM,). Thus we must assume that the single specimen of Dytiscus unistriatus personally studied by Schrank is lost.