122 

 Stophombna Philomela. (Billings.) 



Stkophomena Phioomki.a. — Canadian Naturalist and Geologist, Vol. V., p. 56, Feb. 1860. 



MS© 



Fig. 100. 



Fig. 101. 



Fig. 100. — Strophomena Philomela. 



101. — The same with a mesial fold. 



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

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

 other; front iiiaj'giu and angles regtdarly 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 ex«ctly like those of the convex form of St. alternata. The 

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

 one-fourth to one-tliird 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 \eutral valve. 



The area of tlie 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 mai-gins. The foramen appears to be almost completely closed, 

 but this charaetev has not been ascertained vrith 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 doe.^ not djfier from that of S. alternata, so far as I have 

 been able to a-suertain. 



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 difler sufficiently to constitute a distinct species. Another 



