1836.] in the Society's Museum. 743 



present, considering that a similar variation of character in Trochus 

 and Helix has not prevailed to separate species from those genera, I 

 have not thought it necessary to detach PI. trochoideus from Planor- 

 his, but am inclined to consider it as one of the terminal species ; 

 merely prefixing to each of the characters above quoted the word 

 " crebrius." 



As this form does not belong to the Silhet collection, and is an 

 inhabitant of the neighbourhood of Calcutta, I intended to have in- 

 cluded it in a paper on some other new Bengal species ; but as it is 

 desirable, in consideration of its interesting and anomalous structure, 

 that its publication should not be delayed until I can devote leisure to 

 their description, I seize the present opportunity for making it known. 



The only specimens met with were taken by me, in August 1835, 

 in the gardens of Barrackpur Park, near a tank, on the margin of 

 which are some artificial ruins. They inhabited large earthen vessels 

 filled with water, containing aquatic plants, and adhered to the prone 

 surfaces of the floating leaves in company with a small Planorbis*, 

 and a small -lengthened Lymnsea which approaches in its characters to 

 L. chlamys of this catalogue. 



21. Planorbis compressus, Hutton, J. A. S. vol. iii. p. 91, No. 12. 

 The Silhet specimens scarcely differ from weathered individuals of 



Lieut. Hutton's shell, in which the extremely delicate carina, which 

 margins the angular periphery in perfectly fresh specimens, is more 

 usually found to be obliterated. The depressed whorls are equally 

 visible on each side, and are highly polished in recent examples. 

 They occur in great perfection near Bandras, adhering to the floating 

 foliage of Trapa natans, and occasionally swimming at large on the 

 surface of jhils. This is the species alluded to by me as Planorbis 

 B. in page 264, vol, i. Gleanings in Science, and figured as No. 10, 

 Plate VIII. 



22. Planorbis Indicus. PI. corneus ? Hutton, J. A. S. vol. iii. p. 

 90, and Benson, Gleanings in Science, page 264, Plate VIII. fig. 6. 



Testa discoidea, albida vel cornea, superne piano, suturis excavatis, 

 umbilico depresso ; subtus planato-depressa, late umbilicata ; anfrac- 

 tibus ventricosis transverse profunde et eleganter striatis setate vari- 

 cibus munitis. Apertura rotundata, auriformi, minime obliqua. 



PL Indicus is scattered over the whole of the Gangetic provinces, 

 and scarcely a pool of water can be found destitute of it. The Silhet 

 specimens prove to be a small corneous variety occasionally to be 



* I omitted to take specimens of this shell, which is either PI. compressus of 

 Hutton, or anew Calcutta species, PI. nanus mihi, which is very similar to the 

 British species PI. albus. 

 5 d 2 



