«W» PAL5:0NT0L0GY OF NEW- YORK. 



Nucleosplra elegans ( n. s.)- 



Plate XXVIII B. Fig. 10 - 15. 

 Shell suborbicular, wider than long. Ventral valve gibbous, particularly 

 towards the umbo, with a flattened or sometimes depressed mesial line 

 down the centre : beak elevated above that of the opposite valve, and 

 incurved ; area sometimes well defined. Dorsal valve depressed convex, 

 somewhat gibbous towards the beak, with a narrow depressed mesial 

 line above, which becomes a broad depression below, producing a gentle 

 sinuosity in the outline of the front : beak small, closely incurved 

 beneath the beak of the opposite valve. 

 Surface of shell finely and beautifully punctate, and sometimes pre- 

 serving remains of the pilose covering. 



This species is distinguished from the preceding by its larger size, greater pro- 

 portional Avidth, unequal convexity of the valves, and the broad scarcely defined 

 depression towards the base of the dorsal valve. A single large specimen, which is 

 more depressed than usual towards the base of the dorsal valve, has a width of 

 almost three-fourths of an inch by a length of half 'an inch. In the ordinary 

 apparently full-grown specimens, the length and breadth are about as four to five. 

 From the form of this species, and from the much greater convexity of the ventral 

 valve and the apparent area, it may be mistaken for Orthis, which it much resembles, 

 more particularly when the valves are a little separated at the hinge line. It may 

 be readily distinguished by the punctate surface, absence of striae, and, internally, 

 by the presence of spires. 



The internal spires, not only of this species, but of the JV. vmtricosa^ frequently 

 appear to be displaced, or to lie obliquely in the valves. In fig. 14, the turns of the 

 spire are vertical to the direction of the valves, the view being from the ventral 

 side. 



Fig. 10 a, h. Dorsal and ventral views of a very symmetrical specimen of the ordinary size, 

 showing slight indications of the central flattening or depression. ( From the 

 Helderberg mountains.) 



Fig. 10 r, d. Front and profile views. 



Fig. 11 a, b. Dorsal and ventral views of a specimen which is proportionally broader. ( From 

 the Lower Helderberg group, Maryland.) 



Fig. 12 c. Dorsal view of a specimen without mesial depression, and showing an extension in 

 front. 



Fig. 13 a, 6. Dorsal and front views of a large individual which is proportionally very broad 

 and deeply depressed in front, showing a broadly sinuate outline. 



