Subjainilies, Genera, and Subgenera — Recent and Fossil 119 



club-^licii)ed aiitl placed in a ^^iiigle row on the sperm duct, it is allied to 

 the subfamily Segmentininae. The jirostate differs from the members of 

 both Planorbinae and Segmentininae in having the diverticula placed di- 

 rectly on the sperm duct instead of on a separate prostate duct. The 

 presence of the fliagellum on the vergic sac places Drepanotrema near the 

 Euroixnm and Asiatic groups Segmentina, Polypylis, Hippeutis, and Intha. 

 The nature of the rachda also indicates relationship with these groups. 

 Although dei)arting from these groups in having the diverticula of the 

 prostate placed directly on the sperm duct, the other characteristics place 

 the genus in the subfamily Segmentininae with little doubt. 



The form of the shell of typical Drepanotrema bears close resemblance 

 to the edentate Oriental groups of Segmentininae, such as Helicorbis, 

 Intha, and Hippeutis, all having the peculiar embracing whorls so charac- 

 teristic of Segmentina. This feature alone marks the assemblage of genera 

 as of subgeneric solidarity. 



Genus PARAPLANORBIS Hanna, 1922 



Type by original designation Planorbis condoni Hanna 



1922. Paraplanorbis H.'Vnna, Univ. Oregon Pub., I, No. 12, p. 4. Type Planorbis 

 (Par a planorbis) condoni Hanna. As section of Planorbis. 



1934. Paraplanorbis Pilsbry, Proc. Acad. Nat. Sci. Phil., 86, p. 59. Type Planorbis 



condoni Hanna. As section or subgenus of Drepanotrema. 



1935. Paraplanorbis Hexderson, Non-Marine Moll. N. Amer., p. 245. Fossil. Type 



Planorbis condoni Hanna. 



Shell (plate 81, fig. 5) . Whorls rounded on the periphery as in Heli- 

 soma Swainson but aperture not expanded, umbilicus very narrow, and 

 size minute (Hanna, 1922, p. 4, description of subgenus). 



Hanna's description of the species Planorbis condoni is as follows: 

 'Shell ultradextral, planorboid, composed of about four and one-half regu- 

 larly increasing whorls; apical cavity a cone of about 120 degrees. Last 

 whorl slightly angulated about the upper margin and descending slightly 

 at the aperture. Lines of growth fine and even, giving the shell a silky 

 luster. Umbilicus deeply rimate 0.51 mm. in diameter. Aperture roughly 

 triangular but rounded on the outer lip; not expanded or thickened but a 

 dejiression both above and below the periphery. Diameter 2.67 nnn.; 

 altitude 0.35 mm.' 



Geographical and Geological Distribution. Vicinity of Warner Lake, 

 eastern Oregon. Hanna's locality No. 212. Pliocene period. 



Species Considered as Valid. Paraplanorbis condoni (Hanna), geno- 

 type, is the only species ascribed to this originally monotypic genus. 



Remarks. This fossil genus is related to Drepanotrema and is con- 

 sidered a section or subgenus of the genus by Pilsbry (1934, p. 59). While 

 the wiiorls are of a clasping or embracing nature, as is usually the case in 

 Drepanotrema and its allies, the spire (left side) appears entirely different, 

 the depression being narrow and the whorls deeply immersed. In view of 

 the difficulty in this family of placing a group in its correct position in the 

 classification by the shell alone, it would seem that the interest of nomen- 

 clature is best served by considering Paraplanorbis a separate genus of 

 Segmentininae related to Drepanotrema. Its geographical location, also, 

 so far removed from the present day distribution of Drepanotrema, is 

 another reason for such procedure. 



