586 , NEW YORK STATE MUSEUM 



Plectoceras jason Billings (sp.) 



Page 484 

 See pi. 30 ; 31 



I Exterior view of a large specimen, exhibiting the rate of growth 



and costae 

 The original is from the lower Chazy limestone (B^ of the section 

 on page 398) at the Valcour shore and now in the New York 



State Museum. 



