Silurian Fossils of Canada, 61 



Ventral valve depressed convex near the beak, and concave all 

 round near the maro^in, area about one line wide and forming an 

 angle of about 115^ with the plane of the lateral margins. For- 

 amen not observed. 



Suiface marked with fine radiating striae, ten or twelve in the 

 width of one line, every third, fourth or fifth one of which is 

 twice the size of the intermediate fine ones. The whole surface 

 is besides (in most specimens) ornamented with indistinct con- 

 centric wrinkles from one fourth of a line to two hues in width. 

 There are probably fine concentratic striso, although I have not, 

 (owing to the partially exfoliated state of the specimens examined) 

 been able to detect them. 



This species varies considerably in the amount of the convexity 

 of the dorsal valve and in the size of the mesial fold in front 

 Some have a wide flat space in the umbonial region, and in such 

 on a side-view, the outline of the shell rises from the beak at an 

 angle of about 45^ onh', while in others, which are more ventri- 

 cose this angle is full 60^ with the plane of the margin. 



Sometimes the sides are strongly compressed, so that the shell 

 becomes subcylindrical and greatly produced in front, the length, 

 exceeding the width. In some specimens the striae are nearly all 

 of the same size, but in general they alternate as in the finest 

 marked specimens of aS^. alternata. 



Resembles S. Thalia, but that species has the ventral valve 

 concave nearly to the beak. It is more uniformly gibbous than 

 S. Jlactuosa, 



Locality and Formation. — Anticosti, Hudson River group. 



Collector. — J. Richardson. 



Dalmanites Bebrtx. N. s. 



Description. — Elongate-oval, tapering from the head to the 

 somewhat pointed tail. Length of the two specimens examined 

 Ij inches each, lengih of head 5 lines, of thorax about 8 lines, 

 of pygidium 6^ lines. 



The head is broadly rounded in front and appears to terminate 

 in short spines at the posterior angles. The glabella is broad in 

 front, narrowed behind and covered with small but prominent 

 rounded tubercles about \ or j\ of a line in diameter and of 

 which there are from 10 to 15 in an area of one line square. The 

 anterior lobe of the glabella is transversely sub-oval and its width 

 about equal to the whole length of the head. It is separated from 



