448 NEW YORK STATE MUSEUM 



The living chamber is large, about one third the length of the 

 entire conch. 



The siphuncle is small, about 2.5 mm wide where the conch is 

 15 mm; somewhat variable in its position between the center and 

 the convex (ventral ?) side of the shell but mostly ventrocentren 

 and notably so in the mature part of the shell ; inflated to not quite 

 double its width in an oblique direction [see pi. 16, fig. 5 and text 



fig. 18] • 



Position and localities. In the lower Chazy (Bg and Bo of 

 Valcour section) near Chazy and on Valcour island; especially com- 

 mon in the dove-colored limestone of Little Monty Bay, Isle La 

 Motte and Valcour. 



Observations. Billings has compared his species with O r t h o - 

 ceras an ell us, a Trenton form with angular sharp annulations 

 but also angular interspaces. Two other species with similar annula- 

 tions have been described by Billings himself, viz, O.balteatum 

 and O. perannulatum, both from the Lower Siluric of Anti- 

 costi [1857, P- 318, 319]- But neither of these is figured and the de- 

 scriptions given are insufficient for closer comparison. 



We have long doubted whether this form should not be properly 

 united with the species described by Billings as O . m a r o from 

 the Chazy of the Mingan islands/ which name would then have 

 precedence over Miller's substitute for O. subarcuatum; and 

 indeed we know that geologists who have collected and studied 

 the faunas of the Chazy of the Champlain basin have unhesitatingly 

 referred all their curved annulated shells to O . m a r o , natu- 

 rally not being aware that Hall's incorrect drawing of O . sub- 

 arcuatum has just such an annulated form as a partial basis. 

 Careful comparisons of the measurements of the depth of the 

 cameras, distance and bight of annulations, convexity of septa and 

 amount of curvature between my own material, Hall's type and 

 Billings's types of O. maro have demonstrated that these meas- 

 urements would not bring out sufficient differences for a specific dis- 

 tinction but that a difference which at present can not be neglected 

 is found in the position and character of the siphuncle. The lat- 

 ter, in O. maro is situated near the center but in S p y r o c e r a s 

 c 1 i n t o n i though somewhat variable, nearer to the convex 

 margin and in mature specimens directly submarginal ; in th.e 

 former species I have also found it to be narrower and with but 

 slightly inflated segments while in S . c 1 i n t o n i the segments 

 are nummuloidal. 



1 Can. Nat. & Geol. 1859. 4:461. 



