CHIEFLY OF THE UNITED STATES. 119 



Operculum calcareous, concentrically striate without, granulate within. 



Proc. Acad. Nat. Sci., 1856, p. 110. 



Eah. — Takrong River, Siam, S. R. House, M. D. 



My cabinet and cabinet of Mr. Haines. 

 Diam. -19, Length -32 inch. 



BemarTcs. — Several of this species are before me from Siam. They are well cha- 

 racterized by their hard calcareous operculum fitting exactly into the peritreme. 

 Bithinia is a genus no doubt well separated from PalucUna. I have never seen the 

 soft parts, but the construction of the operculum testifies to its being different. The 

 general form of the shell of this genus is the same with Paludina, but I have seen 

 none longer than half an inch, viz., the B. faculata Beck, from Denmark. 



Bithinia globula. PL 22, fig. 12. 



Testa globosa, palido-oHvaeea, tenui, diaphana, Isevi, imperforata ; spira depressa, ad apicem obtusa; suturis 

 impressis; anfractibus quaternis, ventricosis ; apertura rotundata, inerassata, subreflesa, superne angu- 

 lata, intus albida; columella inerassata. 



Operculo caloareo, Iffivi, marginato. 



Shell globose, pale olive, thin, semitransparent, smooth, imperforate ; spire de- 

 pressed, obtuse at the apex ; sutures impressed ; whorls four, inflated ; aperture rounded, 

 thickened, slightly reflexed, angular above, within wliitish ; columella thickened. 



Operculum calcareous, smooth, bordered. 

 Proc. Acad. Nat. Sci., 1856, p. 110. 



Ecd).— India., W. A. Haines; Tanks, at Calcutta, S. ShurtleflT, M. D. 



My cabinet and cabinet of Mr. Haines. 

 Diam. -15, Length -22 inch. 



BemarTcs. — I have under examination some dozen of this interesting little species, 

 all of which seem to be mature. Its symmetry of form, its round mouth, with a cal- 

 lous border and linear margin, designate a distinct species, and it is much smaller and 

 more globose than the Siamensis herein described. 



ASSIMINEA CARIN-ATA. PI. 22, fig. 1.3. 



Testa regulariter conica, lutea, vittata, subcrassa, uvnbilicata, loevi ; spira ad apicem acuta; suturis parum 

 impressis, infra lineatis; anfractibus instar septenis, planulatis; apertura elliptica, subcanaliculata, 

 intus vittata; umbilico spiraliter carinato; columella incurvata, ad basim subaugulata. 



Shell regularly carinate, yellowish, banded, rather thick, umbilicate, smooth ; spire 

 pointed at the apex ; sutures slightly impressed, with a small line below ; wliorls 



