BEEKMANTOWN AND CHAZY FORMATIONS OF CHAM PLAIN BASIN 477 



Museum of Natural History and the United States National 

 Museum : 



This is a distinct species, the sutures being straighter in the 

 ephebic stage than in true e a t o n i , the venter and sides are more 

 decidedly flattened, and the relative proportions of the last whorl 

 at the same age different. The ventrodorsal and transverse diam- 

 eters are about equal, whereas in e a t o n i the transverse is con- 

 siderably longer than the ventrodorsal in the mesal plane. The 

 amount of involution in eatoni and the depth of the contact 

 furrow in the ephebic stage is also greater. 



Fig. 35 Fig. 36 



Fig. 35 Scliroederoceras cassinense Whitf. (sp.) 



Transverse section. Natural size 

 Fig. 36 Schroederoceras cassinense Whitf. (sp.) 



Enlargement (x 5.4) of portion of longitudinal section, siiow- 



ing the structure of the siphuncle (siphuncular segments 



dotted) 



We have referred several specimens to this species rather than to 

 S. eatoni on account of their straight sutures and the section of 

 the ephebic volution, which possesses about equal transverse and 

 dorsoventral diameters. In one specimen which we figure here the 

 ventral and lateral faces are so strongly developed that very well 

 marked abdominal angles on both sides of the ventral zone or 

 abdomen are formed [sec pi. 20, fig. i]. A transverse section 

 of the same specimen which is also figured here shows the char- 

 acteristic low broad volution of the neanic stage and a higher whorl 

 of the anephebic stage. 



A special interest attaches to another specimen, also here figured, 

 on account of its retaining the finer details of the siphuncular struc- 

 ture. The siphuncle which is propiodorsan in position exhibits very 

 short straight septal necks [sec text fig. 36], which are not longer 

 than about one eighth of the depth of the cameras, the siphuncle 

 wall being formed almost entirely by the secondary siphuncular 

 segments. 



Position and localities. At Fort Cassin Yt. and A^^ of the 

 Fort Cassin beds at \^alcour. 



