No. 109.] 145 



Stropeomena ( Strophodonta) subdemissa ( n. s.). 



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

 greatest breadth, and terminating in distinct angles; in older 

 individuals the form is subcircular, with 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 strise, which probably form crenulations 

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

 by radiating striae, which are distinct near the beak, and bifur- 

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

 they also increase in number by implantation : these are crosssed. 

 by distant 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 

 striae 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 umbonal regions, 

 compressed at the extremities of the hinge ; beak incurved ; 

 cardinal margins having ( three 1 ) 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 



