106 The Molluscan Family Planorbidae 



Geographical Distribution. Polypylis is found throughout much of 

 eastern China and India and on some of the islands lying off the coast of 

 China and India. Its full distribution and the species belonging to it can 

 not be fully known until more of the species from Asia have been anatomi- 

 cally examined. 



Species Considered as Valid. The following species appear to be cor- 

 rectly placed in this genus: 



Polypylis hemisphaerula (Benson) Polypylis swinhoci (H. Adams) 



Polypylis calathus (Benson) Polypylis taia (Annandale and Rao) 



Polypylis lucida (Gould) Polypylis usta (Gould) 

 Polypylis nitidclla (Martens) 



Geological Distribution. Not ascertained. 



Remarks. Polypylis differs generically from Segmentina and Intha in 

 the absence of a penial gland in the preputium. There is some variation 

 in the form of the flagella in the species examined. In hemisphaerula 

 there is but one flagellum on a long duct, while in calathus and taia there 

 are two short flagella as in Segmentina. 



The shell of Segmentina differs notably from that of Polypylis, being 

 flattened with an acute periphery, while the perijihery of Polypylis is 

 rounded and the shell is high. The lamellae within the aperture in 

 Segmentina are three in number, parietal, basal, and upper labial, all trans- 

 verse to the whorl (plate 76, fig. 4). The space between the lamellae is 

 narrow and three-cornered, quite unlike the wide space in the aperture of 

 Polypylis (plate 76, fig. 5). 



The difference between the form of flagellum in the type sjiecies and 

 the flagella of the other species examined from India and China might 

 indicate a division into two groups, as suggested below. 



Group I. With one swollen flagellum on a long duct. 

 Example: Polypylis hemisphaerula (Benson). 



Group II. With two short, narrow flagella without swollen end. 

 Example: Polypylis calathus (Benson). 



Polypylis taia (Annandale and Rao) . 



However, too few of the Asiatic species have thus far been examined 

 anatomically to warrant separation into subgenera at the present time. 



Genus HELICORBIS Benson, 1855 



1855. Helicorbis Benson, Jour. Asiatic Soc. Bengal, XXIV, p. 126. Subgenus of Pla- 

 norbis. No type cited. The species Planorhis (Helicorbis) umbilicalis Benson, 

 one of the original species listed, is here nominated as type of the genus. 



1906. Helicorbis Dall, Nautilus, XIX, p. 105. Considers group equal to Hippeutis 

 {kg.) Charp., 1837. 



1921. Hippeutis Ann.-vnd.^le and Pr.\shad (non Charp., 1837), Rec. Ind. Mus., XXII, 



p. 584. Places Planorhis umbilicalis in this genus. 



1922. Hippeutis Annandale (non Charp., 1837). Rec. Ind. Mus., XXIV, p. 361. 



Mentions Planorbis iimbilicalis Benson as belonging in genus Hippeutis. 



1926. Helicorbis Kennard and Woodward, Syn. Brit. Non-Marine Moll., p. 69. Con- 

 sidered synonym of subgenus Hippeutis. 



1931. Helicorbis Thiele, Handbuch, Teil 2, p. 481. Treated as synonym of Hip- 

 peutis. 



Shell (plate 78, figs. 5-7) . Ultradextral, the body whorl wide and over- 

 lapping or embracing the previous whorl, all whorls visible on upper (right) 



