liEEKMANTOWN AND CHAZY FORMATIONS OF CHAM PLAIN BASIN 459 



equal to about one half the depth of the cameras [see plate 17] ; 

 sutures straight transverse with a broad and low ventral saddle 

 which is divided by a faint median lobe. Shallow broad lateral lobes 

 developed in the ephebic portion. 



Siphuncle tubular, large (one fifth the hight of volution), sub- 

 ventren in nepionic and neanic growth stages, extracentroventren 

 in ephebic stage [see text fig. 22]. 



Shell smooth in ephebic stage, slightly costated in the neanic stage 

 [fide Hyatt] and undulated in gerontic stage. 



Position and localities. Fort Cassin beds at Fort Cassin Vt. and 

 Valcour N. Y. 



Observations. This large sized nautiloid can be distinguished 

 from all other involute associates except E . rotun dus and E . 

 accelerans by its great rate of growth. E. rotun dus dif- 

 fers from E . k e 1 1 o g g i according to Hyatt by its more rapid in- 

 crease in the growth of the dorsoventral diameter and the retaining 

 of the siphuncle near the venter for a longer time. Whitfield had 

 placed this form under Nautilus rather than under Lituites as he 

 had no evidence indicating that the last whorl becomes free and 

 the position of the siphuncle was more suggestive of Nautilus. Hyatt 

 however gives the outline of a specimen which shows a dorsal mar- 

 gin of a free gerontic whorl and we have three specimens which 

 leave no doubt of the evolution of the last whorl. 



Schroder infers from the original drawing of the type specimen 

 that the latter retains the apertural margin and also Hyatt states 

 [p. 442] that " the aperture as figured by Whitfield has lateral crests 

 which are most prominent opposite the centers of the lateral zones, 

 receding into sinuses on the umbilical zones." The retention of the 

 aperture is however improbable in view of the short portion which 

 is retained of the living chamber ; nor does Whitfield mention the 

 observation of the aperture. Inspection of the type specimen leaves 

 no doubt that the aperture is not preserved, and the apparent 

 aperture is but an accidental fracture which does not even run par- 

 allel to the growth lines. I am not aware that the aperture has been 

 observed in an.}' other representative of this species. From the di- 

 rection of the growth lines and undulations we can infer, how- 

 ever, that lateral crests were present similarly as in T a r p h y - 

 c e r a s c h a m p 1 a inense. 



A small collection of cephalopods from the Shakopee formation 

 in Minnesota, in the possession of Dr Sardeson, contains an involute 

 form, preserved in the mold of the first volutions, the living 



