PILSBRY — DESCRIPTION OF A NEW HYDROBIA, ETC. 33 



DESCRIPTION OF A NEW HYDROBIA, WITH 

 NOTES ON OTHER RISSOIDvE. 



BY HARRY A. PILSBRY. 

 Read before the Academy, "July 30th, 188b. 



Hydrobia texana, sp. nov. 



(Plate III., Figs. 1-6.) 



Shell small, conically elevated, rather acute, thin; whorls five to 

 six, convex, lightly striate transversely, with numerous coarse, irreg- 

 ular, revolving striae, becoming less distinct on body-whorl; sutures 

 well impressed; aperture ovate, somewhat angled, posteriorly rounded 

 before; peritreme simple, acute, not sinuous, adherent to body-whorl, 

 sub-reflexed at the narrow but well-defined umbilicus. Epidermis 

 dull greenish-brown or gray; operculum ovate, sub-spiral, corneous, 

 closely fitting the aperture, with coarse wrinkles radiating from inner 

 margins of whorls; polar point close to columella. The measure- 

 ments of three specimens are as follows : 



a. Length, 4.50"""; breadth, 2.5o mm . 



b. " 3-45 mm ; " i.98 mm . 



c. " 4.oo' nm ; " 2.oo mm . 



Habitat. — Guadalupe River and its tributary, Comal Creek, Comal 

 County, Texas. 



The spiral stria? are irregularly developed, the upper ones being 

 most constant. On some specimens there is a more prominent, 

 slightly nodose, revolving line above the periphery. Specimens may 

 be seen in the collections of the Davenport Academy of Natural 

 Sciences, the Philadelphia Academy of Sciences, and of the writer. 

 The revolving sculpture at once distinguishes this species from the 

 Hydrobia seemani of Frauenfeld,* which it resembles somewhat in 

 outline. A comparison with Frauenfeld's figure shows the Texan 

 shells to be of slightly stouter form. It is quite distinct from other 

 described American species. The specimens were found on the 

 under side of stones in rapidly Mowing water. Its associates in Comal 

 Creek are Goniobasis pleuristriatus Say, G. comalensis, sp. nov., and 

 an undetermined Amnicola. 



♦Described from Durango, North-west Mexico. Vide Verh. K. K. Zool.-bot. Ges., Wien, 

 p. 1025, 1863, also p. 505, 1S65 (figured). 



[Peoo. D. A. N. 8., Vol. V.] 5 [July 12, 1887. | 



