115 



LiNGULA FORBESI. (N. Sp.) 

 Fig. 96. 



Description. — Elongate, oval ; front narrowly and regularly rounded; 

 sides gently convex ; apex somewhat acutely rounded. Both valves are 

 rather strongly and uniformly convex. Surface with fine concentric 

 striae. 



Length of specimen of average size, 9 lines ; width about 5 lines. 



Locality and Formation. — English Head, Anticosti ; Hudson River 

 group. And also at Junction Cliff, Anticosti ; in Division 1, base of the 

 Middle Silurian. 



Collector.— S . Richardson. 



Genus Strophomena. 



The following descriptions are copied from a paper published in the 

 Canadian Naturalist and G-eologist, Vol. V., February 1860 : — 



In the Silurian rocks of Canada and the neighboring countries, there 

 are many species or varieties of that group of the genus /Strophomena 

 of which /S. alternata may be regarded as the typical form. These are all 

 closely related, and yet exhibit such differences that only those naturalists 

 who entertain wide views upon the subject of the value and significance of 

 specific distinctions, would feel inclined to unite them vmder one common 

 name. The forms of this group most common in the Lower and Middle 

 Silurian rocks are, S. alter7iata, S. incrassata, S. deltoidea, S. earner ata, 

 S. tenuistriata and some others to be described hereafter in this paper. 

 The first of these ranges from the Chazy hmestone upwards perhaps to 

 the Niagara rocks, but is most abundant in the Trenton limestone and 

 Hudson River group. It is also very widely distributed, as it occurs in 

 all parts of the Continent, where the last two formations have been recog- 

 nized, and is also found in the Lower Silurian in England and Ireland. 

 S. incrassata has exactly the same form as some of the varieties of S. alter- 

 nata but is never, as far as I have been able to ascertain, more than half 

 the average size of this latter species. It seems to be confined to the 

 Chazy and the Black River limestone or the lower part of the Trenton, and 

 has therefore, a geological distribution different from that of *S'. altertiata, 

 a fact which would appear to constitute an additional ground for classi- 

 fying it as a distinct species. S deltoidea is a Trenton hmestone form 

 abundant in certain localities, but not generally distributed. Thus in the 



