222 
PALAEONTOLOGY OF NEW-YORK. 
Mucleospira elegans (n. s.). 
Plate XXYIII 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 width, 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 Or this, 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 strife, and, internally, 
by the presence of spires. 
The internal spires, not only of this species, but of the JV*. ventricosa , 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, b. 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 c, 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, b. Dorsal and front views of a large individual which is proportionally very broad 
and deeply depressed in front, showing a broadly sinuate outline. 
