122 



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STOPHOMENA PHILOMELA. (Billings.) 



STROPHOMENA PHILOMELA. Canadian Naturalist and Geologist, Vol. V., p. 56, Feb. 1860. 



Fig. 100. Fig. 101. 



Fig. 100. Strophomena Philomela. 



101. The same with a mesial fold. 



Description. Shell rather large ; hinge line exceeding the greatest width, 

 forming short rounded ears; sides gently concave, converging towards each 

 other ; front margin and angles regularly rounded, sometimes with a pro- 

 jecting lobe in the middle. Width on hinge line from eighteen to twenty 

 four lines. Length from two-thirds to four-fifths the width. 



In the ventral valve the umbo and depressions on each side are well 

 defined and exactly like those of the convex form of St. alternata. The 

 visceral disc is moderately and broadly convex ; the deflected margin from 

 one-fourth to one-third the whole length of the shell, passing into the disc 

 with a short rounded curve. Dorsal valve with the curvature corresponding 

 to that of the ventral valve. 



The area of the ventral valve is a little more than half a line in height 

 at the foramen in a specimen two inches wide, and it inclines a little out- 

 wards apparently forming an angle of from 160 to 170, with the plane 

 of the lateral margins. The foramen appears to be almost completely closed, 

 but this character has not been ascertained with certainty owing to the 

 imperfection of the specimens examined. The hinge teeth are striated as 

 in S. Leda. The area of the dorsal valve is almost linear, or at the most 

 not half the width of that of the ventral valve. 



The surface does not differ from that of S. alternata, so far as I have 

 been able to ascertain. 



Varieties. One specimen has been found associated with the others of 

 this species in which the length and breadth are almost equal. It has no 

 ears, although it is longer in proportion to the width, and yet it does not 

 appear to differ sufficiently to constitute a distinct species. Another 



