Subfamilies, Genera, and Subgenem — -Recent and Fossil 123 



overlapping whorls of Drcpanotrona. The very long radula sac is also 

 a characteristic feature of the anatomy. 



The radula appears very different from that of Drepanotrema (see 

 plate 68) because of the apparent absence of interstitial cusps between the 

 larger cusps. These might have been present but overlooked because of 

 tiic small size of the radula teeth. The general shape of the mesocone in 

 Odhncr's figure (4) is suggestive of the same cusp in Drepanotrema, but 

 the ectocone and entocone are much shorter. The radula is markedly dif- 

 ferent from that of Tropicorbis. 



Aa^orbis, therefore, appears to be another one of the peculiar groups 

 of South American Planorbidae, related to Drepanotrema, but distinct 

 by both shell and anatomy. 



Subfamily HELISOMATINAE F. C. Baker, 1928 



Prostate diverticula compound or multiple, consisting of a basal stem 

 with branches grouping around a short prostate duct which is in intimate 

 contact with the sperm duct. In cross section, the prostate exhibits a fan- 

 like design. A penial gland is nearly always present with an external duct 

 of greater or lesser length. The kidney is usually heavily ridged. The jaws 

 are sim})le, of three pieces, a superior and two lateral jaws. 



Type genus Helisoma Swainson. 



The groups referred to this subfamily are noted below. 



With one penial retractor muscle: Helisoma and subgenera Seminolina, Picr- 

 osoma and Planorbella. 



With two penial retractor muscles: Carinifex and Parapholyx. 



Without penial gland duct: Planorbarius. 



The fossil groups Vorticifex, Perrinilla, and Pompholopsis are included 

 in this subfamily because of likeness of shell to Carinijex or Parapholyx. 



With the exception of Planorbarius, which appears to have character- 

 istics admitting it to this group, the subfamily is wholly American and 

 is perhaps the most important planorbid element in the North American 

 molluscan fauna. It is widespread throughout the northern part of North 

 America and the species are numerous. 



Genus HELISO:VIA Swainson, 1840 



Type by original designation Planorbis bicarinatus Sowerby (= Planorbis 

 bicarinatits Say = Planorbis anceps Menke) 



1840. Helisoma Sw.\ixsoN, Treat. Malac, p. 337. Type Planorbis bicarinatus Sowb. 



As subgenus. 

 1846. Helisoma Herrm.^nnsen, Ind. Gen. Mai. Prim., I, p. 516. Tj^pe Planorbis 



bicarinatus Say. As subgenus. 

 1865. Helisoma Binney, L. and FW. Sh. X. A., II, p. 112. No type cited. As subgenus. 

 1870. Helisoma Dall, Ann. N. Y. Lye. N. H., IX, p. 351. Type Planorbis bicari- 

 natus Sowb. As subgenus of Planorbis. 

 1872. Helisoma Tryon, Mon. FW. Univ. Moll. U. S., pp. 188, 198. No type cited. As 



subgenus. 

 1880. Helisoma Fischer and Crosse, Moll. Terr. Fluv. Mexico et Guat., II, p. 60. As 



subgenus. 

 1884. Helisoma Tryon, S. and S. Conch., Ill, p. 106. Type Planorbis bicarinatus Say. 



As subgenus. 

 1886. Helisoma Cle.ssix, Syst. Conch., XVII. i). 33. Tyjie Pl((uurbi.'< bicarinatus S:iy. 



As subgenus. 



