a»6 PALiEONTOLOGY OF NEW-YORK. 



UliyiU'lioiu'lla sulcoplicuta ( n. s.)- 



Platk XXXV. Fio. 1 a, b, c. 

 Shell subtriangular, wider than long, compressed. Valves nearly equal : 

 beak of the ventral valve prominent, attenuated, acutely pointed and 

 arched : beak of the dorsal valve incurved. 

 Surface marked by about sixteen simple longitudinally grooved plications, 

 four of which are very faintly elevated towards the front of the dorsal 

 valve, forming an indistinct mesial fold, corresponding to a sinus in the 

 opposite valve which is occupied by three plications. 

 A marked peculiarity of this species is the longitudinal groove along the centre 

 of each of the plications. Of the four plications elevated on the dorsal valve, the 

 two central ones are less prominent than the others, and separated by a deeper and 

 wider depression which continues quite to the apex of the beak. 

 Fig. 1 a, b. Ventral and front view. 

 Fig. 1 c. Enlargement of the striae. 



Geological position and locality. In the shaly limestone of the Lower Heldei'berg 

 group : Albany county. 



lUiyncIionella forniosa ( n. s.). 



Plate XXXV. Fio. 6 a - y. 

 Shell subtriangular or transversely-oval ; lateral margins forming an angle 



at the beak of about 90° to 110°. Ventral valve somewhat more depressed 



than the opposite : beak prominent, arched, not strongly incurved. 



Dorsal valve larger, declining with a gentle curve towards the margins : 



beak incurved. 

 Surface marked by twenty to twenty-four simple angular plications on 



each valve, from two to four of which in the middle are coarser and 



depressed in the ventral valve, having a corresponding number abruptly 



elevated upon the dorsal valve ; concentrically marked by fine closely 



arranged striae. 



This handsome species may be recognized by the neatly rounded outline of the 

 latero-basal margins, the abrupt sinus, and the stronger central plications. 



A single specimen from the same position as the above shows a less distinctly 

 defined sinus and mesial elevation, with five plications on the latter and four in the 

 former, and only six on each side. I am disposed to regard this as only a variety of 

 the above, though future collections may prove it to be distinct. Fig. 2 a, 6, c and 



