1836.] Fluviatile Shells from Silhet. 357 



the animal, nor does the mantle line the interior surface of the wing-. 

 No organ likely to occupy the sinus is observable either when the 

 animal is crawling or when it is drawn out to its fullest extent. The 

 foot is shorter in proportion than that of Cyclostoma, hardly appear- 

 ing beyond the disc of the shell when the animal is crawling, and the 

 curious cup-shaped operculum is received into the wide vortici-form 

 umbilicus of the shell, which it almost fills, whereas the thin flat 

 operculum of C. involvulus is carried behind the shell. 



My living specimens oiPt. rupestris were taken at Patharghata* dur- 

 ing a morning shower in September. I had in vain searched the ground 

 and bushes among the moist rocks and dripping jungle, where multi- 

 tudes of Cyclostoma involvulus, the reversed Helix interrupta and 

 Nanina vitrinoides were moving about, and had nearly abandoned the 

 search, when I thought of trying an open tract of the hill whence the 

 jungle had recently been cut. Here, on the exposed side of the hill, 

 as well on the bare surface, as under leaves, I at last discovered the 

 sought-for shell. At the foot of the hill a single specimen of a small 

 conoid Helix, which I had recently discovered at Berhampore, was 

 found adhering to the leaves of a shrub. 



Pterocyclos hispidus, is perfectly distinguished from P. rupestris by 

 its greater size, the flatness of its spire, its sculpture, hispid epidermis, 

 retromitted tube, and the inferior development of the adult mouth. 

 Coming from a climate where it enjoys damp throughout the year, 

 it may possibly use the perforation for a breathing hole when its 

 aperture is closed, but in P. rupestris the operculum is drawn in 

 beyond the sinus, so that no such use can be made of it for breathing 

 air, for which, moreover, it has probably little occasion during the 

 season of drought and torpidity. 



18. Pterocyclos parvus. Spiraculum parvum, Pearson, Journal 

 of the Asiatic Society, vol. ii. p. 592. 



This species, which is coloured like one of the varieties of P. rupes- 

 tris, never attains more than half the size of that species. The numer- 

 ous specimens brought from Silhet have all a perfect, reflected peris- 

 tome. It is also distinguishable by the greater tendency of the sinus 

 being often in strict contact, though the circle is never completed by 



* Besides some other plants in flower which I had not leisure to note, I 

 observed a little blue-flowered Tradescantia, a dwarf Ruellia, and a beautiful 

 large-flowered Pesticia with spikes of flowers of a pale verdigris-green colour, 

 which I had only once before seen ornamenting a corolla in a species of Ixia (J. 

 maculata ?) In December 1831, the jungle on the side of Patharghata was flam- 

 iDg with the rich blossoms of Holmskioldia coccinea. On Kotanasi, a hill 

 between Patharghata and Terriagali, I captured a fine specimen of the splendid 

 Buprestis Chrysis, 



