I92T.] 



Manipur Mollusrs. 



583 



Gyraulus cantori (Benson). 



1850. Planorbis cantori, Blmisoii, Aim. Mag. Nat. Hist. (2) V, p. .U9-. 

 1S76. Planorbis cantori, Hanley and Theobald, Condi. Indica, p. xviii, 



and p. 18, pi. xl, figs. i-;,. 

 1878. Planorbis (Segmentina) cantori. Nevill, Hand-list Moll. hid. 



Mus. I, p. 246. 

 1915. Planorbis (Segmentina) cantori, Preston, Fatni. Brit. hid. 



Fresh-if.-Moll., p. 126. 



Benson in his original description of the species specifically 

 mentions partitions or lamellae within the shell ; these like the ones 

 described bv the same author in another species (Planorbis umhi- 



\^ \^---V^te-^ V^ v^ 



B. 



Fig. 16. — Radular teeth of Planorbidae. 



.\. Gyraulus cantori (Benson). 



B. Hippeutis (?) iimbilicalis (Benson). 



licalis) are not to be seen in the specimens which we assign to this 



species. It appears likely that Benson mistook external furrows 



of the shells for internal septa. In other respects our specimens 



agree closely with his description 



and with Hanley and Theobald's 



figures of this species. The shell 



closely resembles that of G. cubhra- 



ticus but is still more depressed and 



flattened and has an even stronger 



peripheral keel. 



The anim.al resembles that of 

 a true Gyraulus in all respects. The 

 branchial process consists of a large 

 and well- developed leaf-like pallial 

 outgrowth in continuation of the 

 left epipodial lobe. It is thick and 

 highly vascular. The pulmonary 

 siphon, which is just internal to the 

 branchial process, is not well devel- 

 oped, and is formed by the epipo- 

 dial lobe itself. 



The radula has the dental for- 

 mula 9.8.1.8.9. The central tooth is bicuspid as other species, 

 but the cusps are rather large and pointed. The lateral teeth 

 are tricuspid with the cusps resembling those of the central. The 



Fig. 17. — Penial st\let of Gyra- 

 ulus cantori (Benson). 



