NATURAL SCIENCES OF PHILADELPHIA. 153 



genus," although the genus is now admitted to extend from Eng- 

 land to India. 



ASSIMINEA CALIFORNIA, n. s. ? PI. 3, Fig. H. 1, 2, 3. 

 ? Hydrobia Califomica, Tryon, Amor. Jouru. of Conch. I. 221, pi. 22, f. 11. 



Sp. en. A. testa parva, imperforata, nitente, sutura bene impressa anfr. 

 vi. convexis, cito crescentibus, ult. tumido ; peristomate acuto, non 

 continno, callo tenui parietali ; colore corueo, ex nigro-brunnescente, 

 operculo pertenui, transluceiite, aufr. ii. et dim. 



Long. 0.14, lat. 0.07, long, spirse 0.025, aperturse 0.06, div. 50. 



Animal albescens, tentaculis et caput antice nigro tincto, regio 

 inter tentaculis rufus. Longitudo bis major quam long, testse. 



Habitat. In ripas aquarum salinarum extrinsii San Francisco, 

 California, inter lapidas, Salicornia, etc. 



Shell very small, imperforate, shining, whorls 6, rapidly in- 

 creasing, rather convex, suture well impressed, body-whorl swol- 

 len, peristome not continuous, acute, with a slight parietal callus. 

 Color dark horn-brown. Operculum very thin, colorless, its whorls 

 2^. Animal whitish, tentacles and muzzle tinged with black, a 

 rufous patch on top of head. When extended it is about twice as 

 long as shell, the foot ovate. 



Inhabits brackish creeks near mouth of San Francisco Ba}-, and 

 found in great numbers within the city limits under small stones 

 with Alexia. The animal crawls actively by a jerking motion, 

 alternately projecting the foot in front of the muzzle and then 

 drawing the shell forward, so as to show the two positions repre- 

 sented in the plate. 



The shell closely resembles Hydrobia Califomica, which is found 

 in similar places at Oakland and Martinez, but, it being rather 

 scarce there, I have not been able to obtain living specimens yet 

 for comparison. Mr. Tryon's description and the dimensions 

 given agree exactby, but Oakland specimens of the shell are thicker, 

 the whorls a little shouldered, and the umbilical region pitted, 

 perhaps from stronger growth. Mr. Tryon's figure, however, does 

 not agree with the dimensions. 



It differs from AJ subrotundata, Carpenter, of the Str. of Fuca, 

 in all its dimensions and in size. (See Ann. and Mag. Nat. Hist.,. 

 1865, p. 28.) Several of our fresh-water Hydrobrinse have been 

 confounded with H. Califomica. 



I believe this is the first of the genus determined to inhabit the 

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