﻿328 CONRAD'S DESCRIPTIONS OF 



CIBOTA, Browne.— BYSSOARCA, Swainson. 



Cibota lintea. PL 34, fig. 11. Rhomboidal, very inequilateral ; sides flattened or 

 slightly contracted, radii minute, close, reticulated, except on anal side, where the 

 radii are wider and smooth ; hinge and basal margins parallel, the latter slightly 

 contracted ; anal margin very obliquely truncated. 



This genus has been named Navicula by Blainville, and Btssoakca by Swainson. 



CUCULL^A, Lam. 



Cucull^ea capax. PL 35, fig. 2. Obliquely triangular, inequilateral, profoundly 

 capacious, elevated ; posterior slope flattened, very broad, forming nearly a right angle 

 with the terminal umbonal slope which is abruptly rounded ; valves slightly contracted ; 

 umbo profoundly prominent, beaks distant ; surface reticulated with fine lines, the 

 radii in pairs, most conspicuous posteriorly, largest on the left valve. 



2. CuculljEA tippana. PL 35 fig. 1. Short trapezoidal, inequivalved, inequila- 

 teral, ventricose ; radiating lines numerous, reticulated, most conspicuous on the left 

 valve ; umbo prominent ; beaks rather distant ; cardinal area profound, with three 

 angular impressed lines ; umbonal slope acutely rounded. 



In the specimen figured, the margin of the larger valve is thick, abruptly grooved 

 within, in which groove the margin of the opposite valve is inserted. Allied to G. 

 /Shumardi, Meek. 



DREISSENA, Van Beneden. 



Dreissena tippana. PL 34, fig. 14. Falcate, with distinct lines of growth ; front 

 excavated, the margin acutely angular ; the dorsal and posterior margin form a 

 regular curve ; base rounded ; beaks acute. 



This shell somwhat resembles Dreissena polyniorpha. The hinge is not accessible 

 in the only specimen in the collection. The valves are united and are remarkably 

 perfect. The form is not unlike that of Mytilus falcatus, D'Orbigny. 



PINNA, Un. 



Pinna laqueata. A fragment — ventricose, with eleven prominent, slender ribs 5 

 interstices concave. 



GERVILLIA, Defrance. 



Gervillia ensiformis. PL 34, fig. 10. Ensiform or falcate, profoundly compressed, 

 iridescent ; hinge with about twenty-seven radiating prominent teeth ; cavity very 

 shallow, with an irregular surface, the upper margin angular ; within pearly and 

 iridescent. 



Two valves of this species are in Dr. Spillman's collection, which are both broken 



