BEEKMANTOWN AND CHAZY FORMATIONS OF CHAMPLAIN BASIN 425 



the latter species comes from the neighborhood of Montreal (village 

 of St Eustache) and hence from the northern extension of the 

 Champlain basin instead of the lower St Lawrence gulf, as O . 

 s o r d i d 11 m does, is a further argument for the identity of the Fort 

 Cassin material with O. montrealense. 



Billings has given the following description of the form in 

 question : 



Section circular, smooth, tapering at the rate of about one line 

 to the inch; septa very convex, i8 or 20 to the inch at a diameter 

 of 8 lines ; siphuncle cylindrical, marginal, seven sixteenths the whole 

 diameter of the shell ; surface unknown. 



Whitfield has added the observation that the form has a smooth 

 shell ; and we are enabled to state that the submarginal siphuncle 

 is tubular in form, with slight interseptal con- -- 



strictions, produced by the incurving septal , 



necks, each of which closes the space from one ! 



septum to the next preceding. The septa are i 



very convex, their depth amounting to twice I 



that of the chambers ; the sutures possess a 

 rather deep ventral lobe with an apparent small 

 median saddle opposite the siphuncle [see pi. 9, 

 fig. 8]. The living chamber and aperture, as ' 



well as the apex of the conch have not yet been 

 observed. 



The marginal position and large size of the rr- o c- ^ 



* ^ -^ Fig. 8 Endoceras 



siphuncle, as well as the structure of the si- ™.o V^''^T^'"'■^^ 



^ Bill, (sp ) Longitu- 



phuncular wall leave no doubt that we have here '^.'"^^ section. Nat. 



^ size 



before us one of the primitive forms belonging 

 to the Endoceratidae. It is not certain whether the siphuncle con- 

 tained the internal structures usually found in forms of this group, 

 but the section given by Billings [ibid. fig. lie] would suggest the 

 presence of an endosiphocone in that specimen. The extension of 

 the septal necks to the preceding septa only, excludes this species 

 from the genus Vaginoceras, and the apparent absence of the endo- 

 sipholining from Cameroceras ; by exclusion we, hence, infer that 

 at present it may be best referred to Endoceras. 



Genus suecoceras Holm 



Suecoceras marcoui Barrande (sp.) 



Endoceras marcoui Barrande. Systeme Silurien du Centre de la 

 Boheme, v. 2, t. 3, p. 748, pi. 431, fig. 11-13. 



