PEODUCTELLJE OF THE CHEMUNG GROUP. 
181 
elongating, and finallyJ)ecoming continuous ridges towards the anterior 
margin of the valve. The area, if existing, is not greater than the thick¬ 
ness of the shell, and no evidence of teeth has been observed. 
This species has some resemblance to P. dumosa of the Hamilton group; but 
the costse are more slender, with fewer and more slender spines. The dorsal valve 
is very distinctive in its numerous fine pustules on the inner surface. The form of 
the dorsal valve resembles that of the preceding species (P. striatula) in its form, 
but is at once distinguished by its numerous minute pustules on the inner surface. 
No reniform impressions have been observed. 
In numerous specimens from several localities, this species is very constant and 
well-marked in its characters.' There are, however, a few individuals from a diffe¬ 
rent locality, similar in form, but broader and somewhat flattened or depressed 
along the middle of the ventral valve, while the surface is much more coarsely 
pustulose. 
Geological formation and localities. This species occurs at Chemung-narrows in 
Chemung county ; Randolph and East-Randolph, Napoli, Conewango, New-Albion, 
and other places in Cattaraugus county, New-York. 
Productella costatula, var. strigota. 
PLATE XXVI. 
Ventral valve wide, a little flattened along the middle from the umbo 
to the front of the shell, extremely arcuate, broad and rounded near 
the umbo ; the apex closely incurved. 
Surface of the upper part strongly pustulose in the cast; the pustules 
elongated in the middle, and becoming continuous costse towards 
the front. The dorsal valve, in its interior and casts, is narrowly 
deflected towards the front, coarsely pustulose above, and costate 
towards the margin. 
These forms approach to P. arctirostrata in the ventral valve ; but the. dorsal 
valve found associated with that species is very distinct in form and characters. 
The species, and this variety, bear much resemblance to P. arcuata of the sand¬ 
stones and calcareous beds below the Burlington limestone: the costse in the 
ventral valve of that species are stronger and continued nearly to the apex; 
while the dorsal valve is more nearly flat, and interruptedly costate in its upper 
part, the deflected portion longer, with the costse continuous. 
Geological formation and locality. This form occurs in some sandy beds of the 
Chemung group, near Cadiz in Cattaraugus county, New-York. 
