PRODUCTELL^ OP THE CHEMUNG GROUP. 181 



elongating, and finally becoming 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 valvo 

 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. slriatula) 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. strigata. 



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. 

 SuBFACE of the upper part strongly pustulose in the cast ; the pustules 



elongated in the middle, and becoming continuous costa? 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 costae 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 costaa continuous. 



Geological formation and locality. This form occurs in some sandy beds of the 

 Chemung group, near Cadiz in Cattaraugus county, New- York. 



