33 



Surface (as indicated in casts,) marked by concentric undu- 

 lations only. 



This species differs from the preceding in the more quadran- 

 gular form and erect position of the beaks. 



Geological Formation and Locality. In rocks of the age of 

 the Trenton limestone of New York, at Beloit, Wisconsin. 



AMBONYCHIA attenuata, (n. s.) 



Description. Shell elongate-ovate, widest below the middle ; 

 width a little more than two-thirds the length; attenuate at 

 the beaks ; ventricose in the middle, regularly arcuate from the 

 beak to the base; hinge line straight, a little more than one- 

 third as long as the greatest length of the shell, and very 

 oblique to the axis. Beaks elevated and directed forward, 

 obtusely pointed and incurved at their extremity. Surface 

 character unknown, except a few undefined concentric undu- 

 lations upon the casts. 



This species, in form, is somewhat like A. bellastriata of the 

 Trenton limestone in New York ; but the shell is proportion- 

 ately more elongated, the anterior side straighter and the um- 

 bones and beaks less curved forward. 



Geological Formation and Locality. In the Buff limestone, 

 age of Trenton limestone of New York, at Beloit, Wisconsin . 

 CMector. T. J. Hale. 



GASTEROPODA. 



GENUS PLEUROTOMARIA, De Franc. 



PLEUROTOMARIA niota, (n. s.) 



Description. Shell large, broadly sub-conical, the diameter 

 through the last volution equal to about four-fifths of the hight, 

 consisting of six volutions, which are flattened on the periphe- 

 ry, with a very slightly concave space upon the upper side, 

 extending to the suture ; lower side rounded into the mode- 

 rately large umbilicus, the last volution large and ventricose. 



Surface character unknown, except a few undefined undula- 

 tions near the extremity of the last volution, which are more 

 distinct below than above. 



This species is intermediate in form, between P. subconica 

 and P. bicincta ; resembles the first very closely in general 

 outline, except that the volutions are a little too convex above 

 the centre, and the flattening of the periphery is much great- 

 er than the narrow carina of the species ; and in casts there 

 3gr 



