178 [Senate 



This shell in its delicate spines bears some resemblance to P. hirsutus; 

 but the hinge-line is proportionally shorter, the beak much more at- 

 tenuate, the umbo narrower, more ventricose and much more incurved; 

 while the surface is strongly striated longitudinally. 



Geological position and locality. Calcareous sandstone of the Chemung 

 group : Steuben county, N.Y. 



Productus rarispin^ (n. s.). 



Pal. N.Y. Vol.iv. 



Shell semielliptical, length and height nearly equ^l ; hinge-line 

 about equalling the greatest width of the shell : ventral valve 

 extremely gibbous or ventricose; lateral extremities abruptly 

 deflected, and marked by two or three strong concentric folds 

 which become obsolete upon the body of the shell; mesial 

 ^ region broadly flattened or slightly depressed. Surface marked 

 by fine concentric striae, and sometimes apparently by fine 

 radiating stride, the cardino-lateral margins or ears having a 

 few strong spines irregularly disposed : a few scattered spines 

 also mark the mesial depression. 



This species differs from the last in the greater gibbosity of the ventral 

 valve, the deflected cardinal extremities, the broad flattened or depressed 

 mesial region and the scattered spines. It bears some resemblance to 

 DE Koninck's figures of P. orbignianus, but it has fewer spines and no 

 defined sinus. 



Geological position and locality. Shales of the Chemung group : 

 Allegany county, N.Y. 



Productus rarispin^. 



