132 



specimens is that in S. rectus the deltidium of the ventral valve extends 

 down nearly to the hinge-line, and thus almost entirely closes the foramen, 

 while in S. pecten it only closes a small portion at the apex. 



Some of the specimens of S. jyecten have a minute perforation in the 

 beak of the ventral valve, and there are indications of a similar aperture 

 in jS. recta. 



The Russian species 0. asmusi (De Vemeuil) , figured and described 

 in the Geology of Russia, seems to be closely allied to *S'. recta. 



Locality and Formation. — This species has only been found at one 

 locahty in Canada, as far as I am aware, — the top of the Barrack Hill in 

 the city of Ottawa, in the upper beds of the Trenton limestone. 



Collector. — E. Billings. 



Strophomena subtenta. (Com-ad.) 



Strophomena subtenta. (Conrad.) 



Lept^na scbtenta. (Hall.) Pal. N. Y., vol. 1, p. 115, pi. 31b, fig. 9 a 6. 



Fig. 109. 



JRemarJcs. — This species occurs at Anticosti, in the Hudson River 

 group, rarely, only three detached valves having been collected. It is a 

 resupinate form, with a gently convex dorsal valve, and the surface 

 marked by fine romided radiating striae increasing in number by implanta- 

 tion several times between the beak and the front margin, and crenulated 

 by fine concentric striae. The hinge-hne and cardinal angles are strongly 

 corrugated by six or seven short obhque wrinkles. The form and surface 

 markings correspond very nearly with the figures and description given in 

 the work cited. Conrad's specimens were from Cincinnati, most probably 

 from the Hudson River group, and ours is found in the same formation, 

 associated with an abundance of Rliyncli07iella capex, so numerous in 

 rocks of this age in the Western States. 



Locality and Formation. — EngHsh Head, Anticosti. Hudson River 

 group. 



Collector. — J. Richardson. 



Strophomena Arethusa. (N. sp.) 



Description. — Of this shell only three separated valves have been 

 collected, and, although somewhat distorted, and pressed nearly flat, the 

 remarkable characters of the surface show them to be distinct from any 

 described species of the Silurian rocks of America. The form is semi- 



