172 [Senate 



spines; a single row just below and parallel to the hinge mar- 

 gin. 



This little shell is very abundant in the calcareous shales, where the 

 ventral valve is preserved, while I have seen but a few imperfect specimens 

 of the dorsal valve. The abruptly gibbous form, and truncated or im- 

 pressed beak and umbo, are characteristic features. In some larger speci- 

 mens with truncated beaks, from other localities, there are a few elongated 

 spiniferous ridges near the base. It is possible that these may be distinct 

 species. 



Geological position and locality. In the calcareous shales near the base 

 of the Hamilton group : Schoharie and Onondaga counties, and shore of 

 Lake Erie above Buffalo, New- York. 



Productus 



Pal. N.Y. Vol. iv. 



Strophomena pustulosa, Hall : Eep. 4th Geol. Dist. N.Y. 1843, p. 180, f. 4. 

 This small species of productus is scarcely larger than the P. truncaius, 

 but the surface characters and extension of the hinge-line give the shell a 

 very different aspect. 



Productus navicella (n. s.). 



Pal. N.Y. Vol.iv. 



Shell subelliptical, length greater than the width; hinge-line 

 less than the width of the shell : ventral valve extremely 

 gibbous in the middle, abruptly bent downwards in front ; beak 

 extremely incurved; umbo projecting beyond the hinge-line 

 nearly one-third the entire length of the shell. Surface marked 

 by concentric undulating strise and interrupted longitudinal 

 ridges, which are garnished with small, round, abruptly pro- 

 jecting spines, and sometimes with spines between the ridges. 

 The distinguishing features of this species are the elongated form, short 



hinge-line, and extremely incurved beak and umbo. The spines are small 



and rigid, rising abruptly from the surface, and not always upon the short 



interrupted ridges, though usually so. 



In general form and elevation of the beak and umbo, this species is not 



