160 PALAEONTOLOGY OF NEW-YORK. 



Hamburgh (Illinois) and in the town of Louisiana (Missouri), and in the calca- 

 reous beds at the base of the Burlington limostono at Burlington (Iowa). 



In the Tully limestone there is a Very extreme form, which, after careful com- 

 parison, I can only regard as a variety of this species, having the front greatly 

 produced. The beak is extremely incurved, and can only have been minutely if at 

 all truncated. 



Productella spinulicosta. 



PLATE XXIII. 



Productut tpinulicotta : Hau, Tenth Report on the Stat« Cabinet, p. 178. 1857. 



Shell broad, semielliptical or somewhat orbicular ; hinge-line generally 



a little less than the greatest width of the shell. 

 Ventral valve varying in shells of different size, from moderately to 



extremely gibbous in the middle, with the beak strongly incurved. 

 Dorsal valve moderately concave in its upper part, and becoming more 



concave or arcuate towards the front. 

 Surface marked by fine strong concentric striae, which are sometimes 



crowded and wrinkled on the body of the shell. There are several rows 



of interrupted ridges or spine-bases, which in entire specimens support 



slender spines. The ears are strongly wrinkled, and support a row of 



four or five spines just below the hinge-line* 



The distinction between the species and the authentic specimens of P. shu- 

 mardiana is not such as to entirely satisfy me of their specific difference. The 

 specimens originally referred by me to this species are smaller than the prevailing 

 . size of P. fhumardiana at Burlington, Iowa, and some of the younger individuals 

 are somewhat broadly truncated at the apex. The spiniferous ridges are usually 

 longer and more prominent than in the Burlington specimens. 



Geological formation and localities. In the calcareous bands of the Marcellus 

 shale and in the shales of the Hamilton group, on the shores of Lake Erie, Cayuga 

 and Seneca lakes and other places. 



Productella trancata. 



PLATE XXIII. 



Productxu truncattu : IIall in Tenth Report on tho State Cabinet, p. 171. 1857. 

 Strophomena puttuloia : Hall, Geol. Report Ith District New-Torlt, p. 189, f. 4. IS-IS. 

 Not Productui piutulonu : VuiuAva. 



Shell small, concavo-convex : hinge-line equalling or less than the 

 greatest width of the shell. 



