* PRODUCTELLJE OF THE CHEMUNG GROUP. 175 



Dorsal valve large, somewhat regularly and sometimes deeply concave, 



but with barely any indication of sudden deflection to the front. 

 Surface of the casts of the ventral valves finely striate or puncto-striate 

 longitudinally, the puncta more marked towards the base of the valve. 

 The ears are strongly wrinkled, with the bases of several spines upon 

 the folds ; these wrinkles extend in obscure undulations across the body 

 of the shell in its upper part. The entire surface is marked by narrow 

 elongate fossets which indicate the places of the spines, the slender 

 bases of which sometimes remain in the depression : in some indi- 

 viduals, there are oval pustules in place of the fossets. There is no 

 appreciable tendency to elongation of these pits or ridges towards the 

 front of the shell ; nor does the surface become costate towards the 

 margin, as those which I have referred to P. lachrymosa proper, from 

 C hemung-nar rows. 



The dorsal valves, associated in the same beds, are strongly wrinkled 

 on the ears, with the folds faintly marked on the body of the shell, which 

 is studded with numerous scattered shallow depressions corresponding to 

 the spines on the opposite valve. The cardinal process is distinctly 

 four-lobed. 



This is one of the largest forms among the Chemung species ; and I am inclined 

 to believe that it may ultimately be proved specifically distinct from P. lachrymosa. 

 Geological formation and localities. In the light-colored sandstones of the Che- 

 mung group, near Olean ; and in a similar rock at Conewango, and in some de- 

 composing semicalcareous layers at Randolph and East-Randolph, Cattaraugus 

 county, New- York. 



Productella speciosa. 



PLATE XXV. 

 Prodvctut tpeciotut : Hall, in Tenth Report on the State Cabinet, p. 176. 1857. 



Shell broadly ovate, subhemispheric ; hinge-line less than the greatest 

 width of the shell, the extremities obtusely angular. 



Ventral valve ventricose : umbo much elevated above the hinge-line, 

 with the apex closely incurved, regularly arcuate from beak to base and 

 more rapidly curving to the sides, abruptly depressed on the sides of 

 the umbo, and concave* between it and the narrow short ears. 



