BEEKMANTOWN AND CHAZY FORMATIONS OF CHAMPLAIN BASIN 419 



Septa rather strongly concave (depth about one third of width), 

 sutures apparently regularly transverse ; cameras short. 7 to 9 being 

 counted within 20 mm, where the diameter is about 20 mm. 



Siphuncle large, nearly half as wide as the phragmocone ; mar- 

 ginal, in contact with the outer shell ; flatter on the outer marginal 

 side than on the opposite; not projecting apicad beyond the cham- 

 bered portion of the conch. Its apical part mostly solid, apparently 

 by organic deposition of carbonate of lime. 



Position and locality. All specimens were 

 obtained at the so called Spelman ledge near /'}.-! 

 Beekmantown station. This belongs to Brainerd \ 

 and Seely's division D of the Beekmantown 

 formation. 1 A 



Observations. There have been described r ' \M 



no less than 27 species of " Orthoceras " from 

 the Beekmantown formation of Canada and New- 

 foundland. Many of these are based on very 

 imperfect specimens, or even on nothing but 

 siphuncles and the majority are not figured; 

 circumstances which render their recognition 

 quite difficult. By a process of elimination we 

 have concluded that our form approaches the 

 following species : O. explorator, flav- 

 i u s , ordinatum and s a y i , and differs ^ y 

 from all the others either bv not being annulated Fi s- 5 Endoceras (?) 



champlainensesp. 



or bv the depth of its chambers. O . e x p 1 o r - nov - Fragment of com- 



1 r pressed siphuncle, the 



a t o r tapers faster and has a smaller siphuncle most J frequently ot>- 



r r served part of the shell. 



which lies midway between center and margin ; Beekmantown x. v. 



o ' Xat. size 



O . flavins, of which the surface and rate of 

 tapering are unknown, has clearly a smaller siphuncle ; in O . 

 ordinatu m the siphuncle lies nearer to the center ; and O . 

 s a y i is described as being rapidly tapering. 



This form is quite representative ol several peculiarities which 

 any one who, after collecting orthoceratites in young, specially 

 Devonic beds, engages in gathering up these earliest representatives 

 of the straight coned cephalopods can not fail to observe. ( )ne of 

 these is that he finds more frequently the siphuncles than 

 the phragmocones of the earlier forms, while in passing to 

 younger beds, gradually the entire phragmocones begin to 

 prevail. Another is that in these older forms the siphuncles are 

 throughout much larger in relation to the size of the conchs than 

 in the later orthoceracones. 



