Silurian Fossils of Canada. 57 



clines a little outwards apparently forming an angle of from 160° 

 to I'JO^, with the plane of the lateral margins. The foramen ap- 

 pears 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 difter from that of S. alternata, so far as 

 I have been able to ascertain. 



Varieties. — One sj>ecimen 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 specinaen has a rounded fold in the 

 front margin which becomes obsolete at one third the length of 

 the shell. 



This species by its projeciing ears, narrow areas and striated 

 hinge teeth is most closely related to >S^. Leda^ from which it dif- 

 fers in being four times the size. It has so much of the aspect of 

 S. alternata, that at present we have no means of distinguishing it 

 from that species wiihout an examination of the hinge area and 

 teeth. 



Locality and formation. — Middle Silurian Anticosti, associated 

 ■with Pentamerus ohlongiis. 



Collector. — J. Richardson. 



The above four species, S, nitens^ S. Ceres^ S. Leda, and S, 

 Philomela are closely allied to S. alternata. The three following 

 have the ventral valve concave, and belong to a very dilferent 

 group, of which S.filitexta (Hall) may be regarded as a typical 



form. 



Strophomena fluctuosa. N. s. 



Description. — Triangular, or semi-oval, usually widest at the 

 hinge-line, and more or less narrowly rounded, pointed, trilobed, 

 or nasute in front. 



Dorsal valve convex, the visceral disc being in general equal 

 to one third the superfices of the whole valve, nearly flat, the 

 remainder abruptly curved down all round so that the lower 

 half of the length of the shell is sometimes at right angles 

 ■with the upper half. The cardinal angles more or less com- 

 pressed and often a little reflected, usually forming angular or 



