17 



^-^Nucula nasuta.— Shell sub-ovate, abruptly contracted 

 in front ; posterior extremity rounded ; beaks prominent, 

 sub-central ; anterior side shortest, and contracted both 

 * laterally and vertically into a proboscidial extension. Sur- 

 face marked by regular lines of growth, 



Length, *14, width '09 of an inch. 



Locality. — Spergen Hill, la. 



CYPRICARDELLA, Hall. 



GENERIC DESCRIPTION. 



Shell ovate or sub-elliptical and sub-quadrate (sub-equi- 

 lateral), closed. Surface concentrically striated ; hinge of 

 right valve having two cardinal teeth ; the anterior tooth 

 directly beneath the beaks, somewhat strong, triangular ; 

 posterior tooth more slender and turned obliquely back- 

 wards, leaving a triangular pit which is probably occupied 

 by a tooth in the other valve. Anterior cardinal margin 

 with a long narrow groove apparently for the reception of 

 a slender projection of the other valve ; posterior side bevel- 

 led from above, edge thin ; ligament external, occupying 

 a deep cavity ; muscular impressions distinct, shallow ; pal- 

 lial impression simple. 



^ Cypricardella sub-elliptica. — Shell sub-elliptical, ob- 

 liquely truncated at the posterior end ; beaks minute at the 

 apex, rising little above the hinge; umbones sub-gibbous, 

 with an undefined elevation extending obliquely towards the 

 posterior basal margin; anterior end narrower than the pos- 

 terior, rounded at the extremity. Cardinal margin forming 

 an angle with the beak of 25° ; base forming a regular ellip- 

 tical curve. Surface marked by regular, fine, concentric 

 elevated lines which are equal to the spaces between. 

 Length, '19 to *32, width '14 to '24 of an inch. 

 Locality. — Spergen Hill. 



■ Cypricardella nucleata. — Shell inequilateral, sub-quad- 

 rangular, gibbose ; anterior end short, rounded ; posterior 

 end broader, abruptly compressed, vertically truncated at the 

 [Trans, iv.] 4 



