Raymond: Pelecypoda of Chazy Formation. 329 



and only two, or possibly three, show the true exterior outline and 

 contours. 



ModioJopsis fabaforftiis and Conocardiuvi beecheri are rather com- 

 mon, and both belong to the upper division of the Chazy, and so are 

 fairly useful as horizon-markers. Several of the species are described 

 from unique specimens, and the Clionychias and Ctenodontas, which 

 are relatively common, seem to have a long range, and occur at any 

 horizon. 



Historical. 



The Pelecypods of the Chazy have, with the exception of the 

 Bryozoa, been the most neglected of all its fossils. Until the appear- 

 ance of Professor Hudson's paper in 1904, only five species had been 

 described, and of these, tw^o had not been figured. Hall in his descrip- 

 tion of the Chazy fauna in V^olume I of the "New York State Pale- 

 ontology" (1847) did not describe any lamellibranch, but in the 

 "Additions and Corrections" on page 315 he briefly described Am- 

 bonychia mytiloides, an unrecognizable form, possibly the same as 

 Clionychia montrealensis. 



Billings, in an article on "Some Silurian and Devonian Fossils of 

 Canada"^^ described Cyrtodonta snbcarinata from the "Chazy, Birds- 

 eye, Black River limestones, and in the base of the Trenton," at 

 Pointe Claire and numerous localities in the Ottawa Valley. 



The next year, in his "Fossils of the Chazy Limestone"^^ the same 

 author says: "The fossils [Lamellibranchiata] are rare in the Chazy 

 limestone, yet the species seem to be somewhat numerous. I think 

 I can make out 17 species belonging to Ctenodonta, Cyrtodonta, Van- 

 uxemia, Modiolopsis, and probably two or three other genera. As the 

 specimens consist mostly of casts, they must remain undescribed until 

 better can be procured." 



He then describes the following: Modiolopsis parviuscida, Vanux- 

 emia montrealensis, Cyrtodonta breviuscula; and mentions Ctenodonta 

 nasuta, Hall, as occurring in the Chazy. 



It is significant that he does not include in this list the Cyrtodonta 

 subcarinata, described by him the preceding year, and the present 

 writer takes this to mean that on closer study he failed to identity 

 any of the Chazy forms with the shell he described in 1858. The 



^^ Canadian Naturalist and Geologist, Vol. Ill, 1858, p. 433, figs. 5-7. 

 16 Caw. Nat. and Geol., Vol. IV, 1859. 



P 



