No. 109.] 145 



Strophomena ( Strophodonta) subdemissa ( n. s.). 



Shell, when young, semicircular, having the hinge equal to the 

 greatest breadth, and terminating in distinct angles; in older 



^ individuals the form is subcircular,Avith the hinge less than the 

 greatest breadth; and obtusely angular or rounded at the ex- 

 tremities : dorsal valve regularly and distinctly concave ; area 

 rather wide ; ventral valve regularly convex; beak very small, 

 and scarcely distinct from the cardinal margin ; area broad, 

 arcuate and considerably inclined over the hinge, marked by 

 rather strong radiating striae, which probably form crenulations 

 along the hing8-line; no distinct foramen. Surface ornamented 

 by radiating strire, which are distinct near the Ijeak, and bifur- 

 cate so frequently as to diminish in size towards the border ; 

 they also increase in number by implantation : these are crosssed 

 bydisLant concentric wrinkles of growth. There were doubtless 

 also fine concentric striae, which have been obliterated by 

 wearing on the only specimens I have seen. 



Very much like Strophodonta demissa, but has a wider area and the 

 strias less distinct near the beak : it may be only a variety of that species. 



Geological position and locality. Hamilton group : Shore of Lake 

 Erie, Maumee river. 



Chonetes gibbosa ( n. s.). 



Shell semicircular; hinge equalling the greatest breadth, and 

 nearly rectangular at the extremities : dorsal valve unknown : 

 ventral valve very convex in the middle and umboual regions, 

 compressed at the" extremities of the hinge ; beak incurved ; 

 cardinal margins having ( three % ) long slender spines on each 

 side of the beak, which are directed outwards (almost in a line 

 with the hinge?). Surface ornamented by distinct, round, closely 

 arranged stride, which increase both by implantation and bifur- 

 cation; of these, about forty-two to forty-four may be counted 

 at the border : fine undulating lines of growth traverse the 

 shell in the other direction. 

 [Senate No. 109.] 10 



