488 NEW YORK STATE MUSEUM 



ness of our identification. In this case, our specimens demonstrate 

 that the siphuncle is not central in position, as it appears from the 

 original drawing, but submarginal [see pi. 34, fig. 8]. 



The posterior part of the type of Orthoceras subar- 

 cuatum Hall [pi. 7, fig. 3] is also a fragment belonging to this 

 species [see p. 445]. 



Orthoceras diffidens, a species made known by Billings 

 from the Chazy limestone of the Mingan islands is closely related to 

 this form and may be even identical with it. Its rate of 

 growth, the depth of the cameras, the character and position of the 

 siphuncle are almost the same as in our specimens and only the 

 siphuncle is relatively smaller (one third of the width in our form, 

 one fifth in O. diffidens). 



Another similar form, which has been neither figured by Bill- 

 ings nor described in all its details so fully as to exclude any doubts 

 of a correct identification, isO.allumettense. Of the latter 

 species it is stated that it closely resembles O. diffidens, both 

 internally and externally but that it has a wider siphuncle. In the 

 relative dimension of the latter it agrees completely with L . m o n i - 

 1 i f o r m e , but the same is less symmetrical than in our form 

 and the cameras are markedly deeper. 



Family actinocera.tie)J!s.ei 

 Genus cyrtactinoceras Hyatt 



Our collection of Chazy cephalopods contains two cyrtoceraconic 

 forms with highly nummuloidal siphuncles filled 'with organic de- 

 posits. The latter proved to be arranged as rosettes or 

 obstruction rings around the septal necks. This character shows 

 that the species belong to the division Annulosiphonata, while the 

 highly nummuloidal form of the siphuncular segments and the ex- 

 tent and regularity of the filling of the siphuncle place them 

 in the family Actinoceratidae. Also the filling of the cameras with 

 organic deposits — which filling in Actinoceras often goes to such 

 an extent as to solidify the entire shell in old age — is here very 

 noticeable and in one species, the small Cyrtactinoceras 

 c h a m p 1 a i n e n s e , carried almost as far as in the large typical 

 species of Actinoceras from the Lower Siluric of the Lake Huron 

 region. 



Still when compared with the typical Actinoceras with its exces- 

 sively nummuloidal siphuncles as it prevails in and after the Black 



