PALEONTOLOGY OF NEW-YORK. 



Spirifcra niarcyi. 



PLA.TE XXXVn. 

 Spxriftr mareyi : Hall, Tenth Report on State Cabinet, p. 168. 



Shell semicircular or subelliptical in outline, gibbous or moderately con- 

 vex ; cardinal extremities extended, sometimes submucrohate : valves 

 subequaJly convex. Area variable in height. Surface plicated. 

 Ventral valve scarcely deeper than the opposj^te, except in young indivi- 

 duals ; very regularly arcuate, with sides sloping somewhat gradually 

 - from the beak to the cardinal extremities : beak usually prominent 

 and pointed, sometimes incurved. Area variable in height, more or 

 less incurved, often nearly flat, strongly striated longitudinally, the 

 inner portion finely marked by vertical striae ; fissure higher than 

 wide, one-third or more of the upper part closed by a strong transverse 

 plate or septum. Mesial sinus distinct but not deep, rounded or flat- 

 ' tened in the bottom, with subangular margins in the upper part which 



become more rounded near the front. 

 Dorsal valve varying from moderately convex to gibbous, a little flat- 

 tened near the cardinal extremities in some specimens. Mesial fold not 

 very prominent, rounded on the top, distinctly defined at the margins. 

 Area of moderate width. 

 Surface marked by from twenty-four to thirty simple rounded plications, 

 which are little elevated and of moderate strength, crossed by fine 

 concentric lines, and marked (in some of the larger specimens) by a 

 fine longitudinal groove along the middle, or otherwise longitudinally 

 striated : this is not a constant feature. In both valves the sui'face is 

 marked by very fine elongate pustules, which become crowded towards 

 the front in old individuals. This gives a very marked and reliable 

 character when preserved as shown in fig. 18, Plate xxxvii. 

 The species presents considerable variations in height of area in the ventral valv«, 

 which in some specimens is large with an arched beak, and in others narrow with 

 the beak much incurved : in the latter variety, the valve is more gibbous. In 

 the original specimens described, the area is' nearly flat, with its exterior margin 

 sharply defined and the beak little incurved. The shells Vary also in the gibbosity 

 of the valves, in the extension of the cardinal extremities, and somewhat in tb« 

 •trength of the plications. 



