Fcunilij Bulinidae 201 



The nulula formula of Indoplanorbis is 33-1-33 with 140 to 150 rows 

 of teetli. There is some variation among the different rows of teeth, prin- 

 cipally in the nmiiber of accessory cusps in the marginal teeth. The 

 radulae examined were remarkably uniform. The radula figured on plate 

 66 agrees with that described by Rao (1923, p. 204). 



The material examined consisted of six specimens from Hsipaw, North 

 Shan State, Burma, collected by Dr. B. N. Choi)ra and Dr. H. S. Rao. The 

 specimens were received from Dr. B. Prashad of the Zoological Survey of 

 India. 



Geographical Distribution. The genus as represented by the type 

 species, PUniorbis cxustus Desh., occurs throughout the plains of the 

 Indian Empire east of the Indus, in Siam, the Malay Peninsula, French 

 Indo-China, and-Sumatra (vide Annandale). For a more detailed account 

 of the distribution of this group see Germain (1921, pp. 28, 29). 



The number of species or races referable to Indoplanorbis is in doubt. 

 Germain (1921, p. 27) places almost everything under exustus as syno- 

 nyms of that species. Planorbis coromandelicus Sowerby and Planorbis 

 indicus Clessin have been thought to be distinct by some conchologists. A 

 careful study of all names in connection with a large series of specimens 

 from various localities might establish several recognizable forms. 



Remarks. The systematic position of Deshayes' Planorbis exustus has 

 been a matter of interest for a number of years. It is the largest planorbid 

 in India and the shell closely resembles certain species of the American 

 genus Helisoma. An examination of its anatomy led Annandale and Pra- 

 shad (1920) to consider it a new genus and Rao's investigations (1923) 

 strengthened the view of its distinction as a generic group. Baker (1933) 

 stated that it was 'one of the most distinct groups of the Planorbidae, its 

 male complex exhil^iting characters not shared by any other group at 

 present known.' Pilsbry (1934, p. 54) suggests its resemblance to Tropi- 

 corbis, particularly in the form of the penial complex. 



]\Iore recently Larambergue (1939, pp. 291, 294) argues that the genus 

 Indoplanorbis is a group of the family Bulinidae. Little is known concern- 

 ing the anatomy of the majority of the species of this family. Two species 

 have been rather carefully studied, Bulinus contortus of Europe by Lar- 

 ambergue ( 1939) and Isidora globosa from Portuguese East Africa by 

 Connolly. In both of these species, the genitalia are similar to those of 

 Indoplanorbis, especially in the form of the penial complex and the pros- 

 tate (see plate 71, fig. 3 and plate 75 of this work). The most convincing 

 characteristic is the pseudobranch, which is lobed in Bulinidae (Germain, 

 1931. p. 514). In Isidora globosa the lobed condition is well shown in Con- 

 nolly's figure (plate 71, fig. 5, of this work.) 



The anomaly of a distinctly i^lanorboid shell in a group made up 

 almost exclusively of physoid shells is no greater than is shown in the 

 American subgenus Seminolina where one species, Helisoma duryi semi- 

 nolina, contains all shapes of shell from distinctly physoid to normally 

 planorboid. The shell of Indoplanorbis exustus is distinctly sinistral, par- 

 ticularly so in the young and immature stages of growth. 



The writer agrees with Larambergue in the statement that the group 

 Indoplanorbis is a distinct genus of the family Bulinidae, the deciding 

 features being the lobulated pseudobranch and characteristics of the male 

 genitalia, particularly the penial complex. 



