The concept of the nominal species Hydrobia semiconvexa Sandberger, 1875 is fixed with the designation of a lectotype, which is figured. The synonymy and proven occurrences of this taxon are briefly reviewed.
During the work on a catalogue of the type specimens of fossil non-marine gastropods present in the Staatliches Museum für Naturkunde in Stuttgart (SMNS) (Salvador et al., this volume) it emerged that the type series of the nominal species Hydrobia semiconvexa Sandberger, 1875 consisted of four different species which are not even congeneric. Since the desired lectotype is not stored in the Stuttgart museum, but in the Städtisches Museum Wiesbaden (MUWI), it is designated in this separate short note.
“Hydrobia” semiconvexa Sandberger, 1875
non 1852 Litorinella acuta Alex. Braun”. - Krauss, p. 142. [non Cyclostoma acutum Draparnaud 1805]
*v 1875 Hydrobia semiconvexa Sandberger, p. 561. [Kirchberger Schichten; partim, excl. syn. Litorinella acuta sensu Krauss 1852]
v 1926 Hydrobia semiconvexa. - Wenz, p. 1931–1933. [part, locality Leipheim only; remainder not semiconvexa Sandberger, 1875]
1960 Hydrobia semiconvexa. - Schlickum, p. 210, pl. 18, fig. 9. [Jungholz near Leipheim]
1966 Hydrobia semiconvexa. - Schlickum, p. 323, pl. 12, figs. 6–8. [Jungholz near Leipheim]
?1970 Hydrobia semiconvexa. - Schlickum, p. 177, pl. 3 fig.2 [coal exploration wells between Trostberg and Tittmoning, Oberbayern; Kirchberger Schichten]
1971 Hydrobia semiconvexa- Schlickum: 571, Pl.1 Fig. 2–3 [Jungholz near Leipheim]
1973 Hydrobia semiconvexa. - Schlickum & Strauch,in Steininger et al., p.391, pl.2 fig.2 [Leipheim]
v 1989 Hydrobia semiconvexa. - Reichenbacher, pl. 2, fig. 8. [Leipheim]
2005 Hydrobia cf. semiconvexa. - Kowalke & Reichenbacher, p. 619, fig. 5(3-4) [Leipheim]
Original diagnosis: “Hydrobia semiconvexa n. sp. (Litorinella acuta Krauss a.a.O. S.142 non Drap. Braun = Hydrobia ventrosa S. 489) ist im ausgewachsenen Zustande bedeutend grösser als die grössten Stücke der H. ventrosa und zeichnet sich durch starke Convexität des letzten Umgangs aus, welcher überdiess ebenso hoch ist als die übrigen zusammen-genommen.“ [English translation: Hydrobia semiconvexa n. sp. (Litorinella acuta Krauss loc. cit. p. 142 non Drap. Braun = Hydrobia ventrosa p. 489) is in its adult state significantly larger than the largest specimens of Hydrobia ventrosa and is characterized by the strong convexity of the last whorl, which, further, is as high as all the remaining ones.]
Remarks: Krauss (1852: 142) described the locality from which he had obtained his material of Litorinella acuta „Alex. Braun” as follows: „Ober- und Unterkirchberg: bläulich-grauer Thon des Fischlagers, mit Paludina conoidea, und wie kalziniert im graulich-weißen kalkigen Trümmergestein mit Planorbis pseudoammonius, Limnaeen, Anodonten und Paludina tentaculata).“ [English translation: Ober- and Unterkirchberg, bluish-grey clay of the fish layer, with Paludina conoidea, and looking as if burnt within the greyish-white calcareous brecciated rock with Planorbis pseudoammonius, limnaeids, anodonts and Paludina tentaculata [now: Ctyrokya conoidea (Krauss, 1852), Planorbarius cornu (Brongniart, 1810), Lymnaeidae spp., Unionidae spp., and Bithynia spp., see Schlickum 1963.]
Type material: The origin of Sandberger's material was said to be the Kirchberger Schichten, without citing a locality. The type series obviously consists of Sandberger's own material and of Krauss' material, because the latter is included by bibliographic reference (article 188.8.131.52 ICZN):
1) Originals of Krauss (1852) in SMNS collection, three lots (see Salvador et al. 2016, pl. 8, figs. 4–5) for details and an illustration. These lots consist of mixtures of Nematurella zilchi Schlickum, 1960, Ctyrokya conoidea (Krauss, 1852) and Bithynia glabra (Zieten, 1832). Two of them bear Sandberger's label, the third one (SMNS 106428) with a label from Krauss is Nematurella zilchi only, which fits best with Krauss' description of “Litorinella acuta”.
2) Originals of Sandberger (1875) in Museum Wiesbaden (MUWI): Nine specimens (originally ten). Sandberger's label reads: “Hydrobia semiconvexa Sandb. Leipheim”.
Only Sandberger's own lot is conspecific with “Hydrobia” semiconvexa as interpreted by Schlickum (1960) and all subsequent authors. Furthermore, it agrees best with his diagnosis. As the type series contains four species, the species concept of Hydrobia semiconvexa Sandberger needs to be fixed on the basis of Sandberger's own material and hence a lectotype is hereby designated as follows:
Lectotype is the specimen illustrated here in Fig. 1, with the following dimensions: height 5.48 mm, width 2.94 mm. It is stored in the Städtisches Museum Wiesbaden, inventory number MUWI-MWNH-TER-1672. Eight lectoparatypes are from the same lot and bear the inventory number MUWI-MWNH-TER-1673.
Type locality: Leipheim (Germany, Bavaria, ca. 18 km E Ulm).
Type horizon: Kirchberg Formation (Early Miocene, Ottnangian, mammal zone MN 4b).
Distribution: To date, Hydrobia semiconvexa is only documented from the Kirchberg Formation in the Leipheim area. Occurrences in “Kirchberg” (now Illerkirchberg), which was incorrectly designated as type locality by Wenz (1926), refer to Nematurella species, mostly N. zilchi Schlickum, 1960. The latter species was not before 1960 recognized as a separate species, and many pre-1960 reports (pre-1921 reports compiled by Wenz 1926) of Hydrobia semiconvexa from the Kirchberg Formation are based on this and possibly other hydrobioid species. Even the report of this species by Schlickum (1970) from Oberbayern is doubtful, on account of insufficient preservation and distance from the type locality. Reports of occurrences outside the Kirchberg Formation need as well to be re-evaluated in the light of the unclear identity of “H.” semiconvexa prior to Schlickum's re-definition in 1960.
Systematic remarks: Hydrobia semiconvexa cannot be placed in the genus Hydrobia s.str.; the citation as “Hydrobia” follows the rationale proposed by Kadolsky (2008).
I thank Drs F. Geller-Grimm and R. Mentzel (both MUWI) for making Sandberger's material available for study, and for the information on the origin of the labels, respectively.