Fossils of the Chazy Limestone. 443 



In two of the specimens there is evidence of a very slight me- 

 sial sinus along the middle of the dorsal valve. 



Closely allied to 0. yrandceva of the calciferous sandrock, but 

 differs therefrom by being more closely ribbed. Should it, how- 

 ever, turn out that this species has a closed foramen, it may 

 perhaps be united with . grandceva. 



Locality and formation. — Mingan Islands. Chazy limestone. 



Collectors. — Sir W. E. Logan. J. Richardson. 



Genus Strophomena. 



Fossils of this genus have as yet been only rarely seen in the 

 Chazy limestone in Canada and such as we have collected are 

 with the exception of some half dozen specimons, in a very bad 

 state of preservation. I think, however, that I can recognize the 

 following : — 



Strophomena incrassata. (Hall) — This shell in external form 

 exactly resembles some of the smaller varieties of S. alternata, 

 but, in the interior of the dorsal valve the muscular impressions 

 are divided by two or three rather strong elevated ridges on each 

 side, a character which appears to show that it is a distinct spe- 

 cies. It occurs in the Chazy limestone at the Mingan Islands, 

 and in the Black River limestone at the Fourth Chute of the 

 Bonnechere. Specimens from the latter locality agree precisely 

 with those sent me from Tennessee by Prof. Safford. The speci- 

 mens from Mingan are a little more convex. 



Stophomena alter nata. (Conrad) — Occurs at Mingan, and I 

 think near Montreal also in the Chazy. 



There are two other species, one of which is resupinate like 

 b.planumbona, but more specimens are required before they can 

 be determined. 



Rhynconella orientalis. (N.s.) 



J, c l 



Fig. 21. 



Fig. 21. — The above figures represent the different views of two 

 specimens of R. orientalis. 



