142 NEW YORK STATE MUSEUM 



The depth of the cameras increases but little in the specimen and 

 they remain relatively shallow as they had been found to be in the 

 smaller specimens; the lateral lobe of the later sutures is apparently 

 a little higher than in the earlier ones. 



The species was cited in Bulletin 90 as coming from the lower 

 Chazy of the Valcour section. The specimens described had been 

 obtained by Professor van Ingen and the writer in the beds out- 

 cropping along the shore of Lake Champlain north of Valcour 

 (Sibley's) dock. These beds were in preceding publications referred 

 to the lower Chazy on lithologic grounds but fossil lists since pub- 

 lished by P. E. Raymond (Annals of the Carnegie Mus., vol. 3, 

 No. 4) show that they belong with the middle Chazy (see op. cit. 

 p. 574). Doctor Raymond cites P. jason from B120 (op. cit. p. 

 535), i. e. the beds just across the bay north of Sibley's dock; B124, 

 the rocks at lake level on the shore at Day's Point; and his station 

 B128, exposures in the large quarries near the road between Valcour 

 and Day's Point. Our records show the species to have been found 

 in beds approximately corresponding to Raymond's stations between 

 these two points. In all the stations where it has been found it is 

 associated with faunas which, although lacking the M a c 1 u r i t e s 

 magnus, are of middle Chazy aspect, the beds in the quarries 

 representing Raymond's zone 2a or the M a 1 o c y s t i t e s 

 murchisoni zone of his division 2 (middle Chazy). If 

 Plectoceras jason is here a middle and possibly upper 

 Chazy form, its range agrees with that observed in its type locality, 

 the Mingan islands. 



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