129 



is gently convex and shaped like that of S. alternata, but the shell is 

 usually suddenly bent, and the deflected margin greatly, produced 

 often at a right angle to the upper part. The length of the margin and 

 the angle of curvature vary extremely. The surface is covered with fine 

 rounded or sub-angular striae, which are always more or less flexuous. In 

 some, they are of a uniform size all over ; in others, they alternate in 

 size, and have from two to six smaller between each two larger. These 

 are crossed by fine concentric striae, and often the visceral disc exhibits a 

 number of obscure concentric undulations, as in iS. deltoidea. The shell 

 has a silken lustre, in certain conditions of preservation. Our specimens 

 agree so nearly with the descriptions of S. imbrex, that for the present it 

 would not be advisable to give it a new name. tS. earner ata (Conrad) 

 appears to be the same species, only smaller and found at a lower horizon, 

 i.e., in the Trenton. 



Locality and Formation. This species occurs in great abundance at 

 Cape Robert, Anticosti; in the Hudson Eiver group. It is there 

 associated with S. Hecuba. 



Collector. J. Richardson. 



STROPHOMENA ANTIQUATA. (Sowerby.) 



Fig. 107. 

 Fig. 107. 8. antiquata. a, dorsal, and 6, ventral views. 



Remarks. This species belongs to the resupinate group along with 

 S. filitexta and S. planoconvexa. The ventral valve is gently concave, 

 and the dorsal as gently convex. The surface exhibits several concentric 

 squamose ridges of growth, and is covered with strong rounded and rugged, 

 often flexuous radiating ridges, which increase both by subdivision and 

 intercalation. Between these larger ridges there are from two to six 

 smaller radiating striae, the whole crossed by very fine concentric lines 

 and irregular undulations of the shell. 



It is with much doubt that I refer our specimens to this species. I 

 have not access to any detailed description except that given by McCoy 



