182 
PALAEONTOLOGY OF NEW-YORK. 
Productella arctirostrata. 
PLATE XXVI. 
Productus arctirostratus : Hail in Tenth Report on the State Cabinet, p. 177. 1857. 
Compare Productella shumardiana of the Hamilton group, page 157 of this volume. 
Shell subovate, extremely ventricose, the proportions of length and 
breadth variable: hinge-line usually a little less than half the width 
of the shell. 
Ventral valve gibbous or ventricose : umbo very prominent and arching 
over the hinge-line, flattened or slightly depressed in the centre, ab¬ 
ruptly depressed at the sides, and extended into short ears at the car- 
N dinal extremities. 
Dorsal valve moderately concave in the upper part, abruptly deflected 
towards the front, and following the curvature of the ventral valve. 
Surface covered by close concentric striae, with a few strong wrinkles 
on the ears; and these are more or less distinctly shown, extending 
across the shell, or marking the surface of the cast. The bases of a few 
spines are usually seen on the ears of the ventral valve, and the umbo 
and upper part of the shell are marked by short spiniferous ridges. 
These ridges become elongated in the lower part of the shell, and 
are finally almost or quite continuous towards the front. The dorsal 
valve is similarly marked; the concentric wrinkles extends across 
the shell, and the spine bases, which are mere nodes in the upper part 
of the valve, become elongated towards the front. 
The casts of the dorsal valve show a bilobed cardinal process, but its 
character cannot be fully made out. The casts of the ventral valve show 
small cavities, from the removal of the dental lamellae, and there is an 
extremely narrow area visible. 
The figures 19-21, illustrate the ordinary form of the ventral valves as they occur 
in casts in sandstone. Figures 16 and 17, are of the interior, and a profile view of a 
dorsal valve. 
Figures 22 and 23, are of a ventral valve and profile of the same, which is a large and 
somewhat extraVagant form. The flattening of the upper part of the valve is continued 
in a broad depression to the lower part of the shell. 
