I ©4 
PALAEONTOLOGY OF NEW-YORK. 
become elongated below, with numerous oblique wrinkles. It is equally difficult 
to unite these with typical forms of P. shumardiana, though ultimately all these 
varieties may be found to constitute only phases of a very variable species. 
Some examples of dorsal valves, similar to the typical forms of P. exanthamata, 
have been found in the Chemung group ; but all these are moderately concave, 
and never approach the form of typical P. shumardiana. 
Geological formation and localities. In the shales of the Hamilton group, on the 
shore of Seneca lake ; and at Tinker’s falls, Onondaga county. 
Productella tullia (n. s.). 
PLATE XXIII. 
Shell broadly ovate, subhemispheric; hinge-line equalling or a little 
less than the greatest width of the shell. 
Ventral valve ventricose with the apex extremely incurved, and much 
produced in front. 
Dorsal valve more or less gibbous, often moderately concave in the 
upper and middle portions, and abruptly deflected and produced in 
front. 
Surface of ventral valve marked by scattered slender spines. Specimens 
of the dorsal valves are nearly all of the interior, strongly wrinkled 
on the hinge-line, with numerous pustuliform elevations,‘which be¬ 
come elongated on the front of the valve. Between these stronger eleva¬ 
tions are numerous fine and sometimes coarser radiating striae which 
become more distinctly visible as the shell is exfoliated from the 
inside, showing that they pertain to the exterior surface. The cardinal 
process is bifurcate, and of considerable length. 
The interior of the dorsal valve is recognized by numerous pustuliform ridges 
and distinct intermediate striae, the latter a character not observed in any other 
species. 
The figures 41-44 illustrate the usual form and features of this species as it occurs in the 
Hamilton shales. 
Geological formation and localities. In the Hamilton group, near Tully and 
Delphi falls in Onondaga county. A single dorsal valve of larger size and mode¬ 
rate convexity is from the Tully limestone. 
