Subfa/nilies, Genera, and Subgenera — Recent and Fossil 129 



Geological Distribution. Miocene?, Pliocene to Recent fauna. 



Remarks. Typical Hclisotua is characterized by a short and wide, some- 

 what bulbous penial complex without a notable constriction between the 

 preputium and the vergic sac. There is a cup-shaped penial gland with 

 a short, narrow, almost straight penial gland duct. The prostate and ovo- 

 testis are made up of many small diverticula radiating from a duct in fan- 

 like i)attern when seen in cross section. Helisoma differs from Pierosoma 

 in its shorter penial gland duct, wider and shorter vergic sac, and generally- 

 different penial complex. From Seminolina, which resembles Helisoma in its 

 short i)enial gland duct, it differs by its shorter duct. The radular teeth 

 also differ from Seminolina in having the cusps sharply aculeate instead 

 of rounded. The' shell of Helisoma is also quite different from Pierosoma 

 and Seminolina in its general bicarinate form with the spire and umbilicus 

 both deeply concave. 



As a subgeneric name, Helisoma has been known in molluscan litera- 

 ture for many years. Binney (1865, p. 112), Tryon (1870, p. 188), and 

 Dall (1905, p. 81) cite the name, using, however, onlv characteristics of 

 the shell for its distinction. In 1926 (p. 201) and in 1928 (I, p. 311), Baker 

 elevated the group to generic rank, basing the distinction on the peculiar 

 genital complex of the male organ. In 1931 (p. 584), the genus was diag- 

 nosed by Baker and the distinctions of the genitalia described and figured. 



Authors generally have misquoted the type of the genus. The Planorbis 

 bicarinatiis of Sowerby, while with little doubt the same as Planorbis bi- 

 carinatus Say, has nothing to do with Say's species and Sowerby was 

 probably not aware that there was another bicarinatus. Dall (1905, p. 84) 

 cited the type as Planorbis bicarinatus (Say) Sowerby, which is incorrect, 

 although the type is correctly cited on page 81. The citation of Planorbis 

 bicarinatus Say, as has been made by some authors, is also incorrect. Say's 

 species dates from 1817, Sowerby 's from 1824. 



A careful study of Sowerby's description and his two figures on plate 

 clxxvii (fig. 4) leaves little doubt about the unity of his species with that 

 of Say. Binney (1865, p. 124) thought it might be Planorbis campanulatus 

 Say, but both figures and description point to bicarinatus. Binney based 

 his opinion evidently on the lower fig. 4 of the plate, which is not clear, 

 and might be mistaken for cam'panulatus. There is little question about 

 the upper figure being intended for bicarinatus. Unfortunately this appro- 

 priate name can not be used, as it is preoccupied for a Paris Basin fossil. 

 Conrad's Planorbis antrosus 1834 has been used in place of bicarinatus, 

 but ]\Ienke's name precedes this by four years and must be accepted. 



Regarding the name Helisoma, it is a Greek noun in the neuter gender 

 and all specific names must, of course, also be neuter (H. B. Baker, 1930, 

 p. 139). 



Subgenus SEAIINOLINA Pilsbry, 1934 



Type by original designation Helisoma scalare (JajO 



1870. Amcria Dall, Ann. N. Y. Lye. X. H., IX, ]>. 356. Example Phym scalaris Jay 

 (non H. and A. Adams, 1855). 



1886. Thomsnnia Axcey, Le Xaturali.><te, Mil, p. 358; not of Signoret, 1879 (He- 

 rn ipt era). 



1931. Thnmsonia Thiele, Handbiich, Teil 2, p. 479. Type Planorbis scalaris (Jay). 

 As section of Planorbis. 



1934. Seminolina Pilsbry, Proc. Acad. X^at. Sci. Phil.. 86, p. 31. Type Helisoma 

 scalare (Jay). Anatom3^ As subgenus of Helisoma. 



