54 Silurian Fossils of Canada, 



Locality and Formation. — This species occurs at Charleton 

 Point, Anticosti, in the upper part of the Hudson River group. 

 Collector. — J. Richardson. 



Strophomena Ceres. N. s. 



Description. — Semi-oval, sides rather straight and a little con- 

 verging for one third their length ; front angles and margins 

 broadly rounded. Width on hinge-line twelve to fifteen lines ; 

 length ten to twelve lines. 



The ventral valve varies greatly in the amount of its convex- 

 ity. In some specimens it is depressed convex, and these have 

 almost precisely the aspect of the more flattened forms of S. al- 

 ternata. Others are strongly convex, nearly hemispherical, uni- 

 formly arched from beak to front, no deflected margin distinct from 

 the visceral disc, the latter occupying the whole of the shell except 

 a small triangular space at the hinge-angles. Between these two 

 extremes there are individuals which present all the intermediate 

 degrees of convexity, and some in which the deflected margin 

 can be detected with a width equal to half the whole length of 

 the shell. 



The surface is the same as that of >S^. alternata. 



The area of the ventral valve is one line high in a specimen 

 fourteen lines wide, and lies very nearly in the plane of the late- 

 ral margin. The foramen is as wide as high, and closed by a 

 strongly convex deltidium, the lower margin of which is concave 

 to admit the equally convex deltidium of the dorsal valve, whose 

 area is almost half a line wide and forms au obtuse angle of 

 between 90^ and 100° with that of the ventral valve. The beak 

 of the ventral valve exhibits in some specimens a small round 

 perforation. 



This species difl"ers from S. nitens ia being in general a little 

 longer proportionally, larger, and more uniformly convex, with 

 scarcely a distinct deflected margin. In S. nitens the length is 

 in general only two thirds of the width, but in this species it is 

 .-always over five sixths. 



The angle formed by the inclination of the areas being obtuse 

 instead of acute furnishes the only character as far as I can ascer- 

 tain by which it can be separated from S. alternata. 



Locality and Formation. — Charleton Point, Hudson River 

 group, and also at East Point in the Middle Silurian, Anticosti. 



Collector. — J. Richardson. 



