226 
PALAEONTOLOGY OF NEW-YORK. 
Spirifera mami. 
PLATE XXXYII. 
Spirifer marcyi : Hall, Tenth Report on State Cabinet, p. 158. 
Shell semicircular or subelliptical in outline, gibbous or moderately con¬ 
vex ; cardinal extremities extended, sometimes submucronate : valves 
subequally convex. Area variable in height. Surface plicated. 
Ventral valve scarcely deeper than the opposite, 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 dr 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 surface 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 xxxvn. 
The species presents considerable variations in height of area in the ventral valve, 
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 the 
strength of the plications. 
