434 



Fossilt of the Chazy Limestone, 



Toronto, has sent us a small slab from the Hudson River groups 

 near Toronto, in which there are numerous impressions of this or 

 a closely allied species. 



Collectors. — A. Murray, J. Richardson, and R. Bell. 



Orthis perveta (Conrad), Orthis sub^equata (Conrad), and 



Orthis gibbosa (Billings). 



Fig. 10. 



Fig. 10. — The above figures represent very nearly the species which 

 I suppose to be Orthis perveta. a } b, and c are figures of a 

 globose form, resembling some of the Tennessee specimens sant 

 me by Prof. Safford, the director of the survey of that State. 



In certain beds of the Chazy limestone there are multitudes of 

 a small Orthis which have, as nearly as I can judge, precisely the 

 form and dimensions of 0. perveta, but, in consequence of their 

 b^ing imbeaded in a rather compact sub crystalline rock, I have 

 not been able to procure any specimens with the surface well 

 preserved. Although it is impossible to determine the species 

 with certainty, yet 1 firmly believe it will, when perfect specimens 

 are procured, turn out to be the true 0. perveta. It occurs in the 

 Chazy limestone two miles north of Montreal, and I have seen it 

 in vast abundance in a rock that crosses the road two or three 

 miles west of the Village of Chazy, in the State of New York. 



Of 0. subcequata I have seen only a single specimen. It was 

 found in an old quarry two miles north of Montreal. 



0. gibbosa was described by me, in the Report for 1856, from 

 specimens collected in the Black River limestone. It is distin- 

 guished from 0. subcequala by having a broad, shallow, mesial 

 sinus in the front half of the ventral valve. It varies greatly in 

 the amount of the gibbosity juid in the length of the hinge-line, 

 which is sometimes only half the whole width of the shell. I am 

 not yet satisfied that it should constitute a distinct species. Prof 



