BEEKMANTOWN AND CHAZY FORMATIONS OF CHAMPLAIN BASIN 499 



remarkable similarity to this species, is Cyrtoceras lati- 

 cnrvatum Whiteaves [1897, p. 224] from the Galena-Trenton 

 beds of the vicinity of Lake Winnipeg. Still the latter species is 

 slightly more curved, has also deeper cameras and is described as 

 compressed in transverse section. 



Ooceras (?) perkinsi sp. nov. 



Plate 34, figure 4, 5 



Description. Slender, small cyrtoceracone with circular sec- 

 tion; attaining in the most complete specimen observed (type speci- 

 men) a length of 75 mm — with the apical end and the living cham- 

 ber missing — and a width of 20 mm; its rate of growth is i mm 

 in 7.5 mm. Its curvature is slight and decreasing in apertural di- 

 rection ; the hight of the arc of the type specimen is 4 mm and its 

 apex is situated at about one third of the length of the fragment. An 

 impressed zone is absent and the living chamber has not been 

 observed. 



The cameras are relatively shallow ; their depth is 3 mm at the 

 smaller end of the specimen and 5.5 mm at the larger, indicating a 

 rather rapid increase in depth ; the sutures are straight and trans- 

 verse ; the septa shallow, their depth amounting to one half that of 

 the cameras and not arching forward to any appreciable amount 

 upon the convex side of the conch. 



The siphuncle is nummuloidal, the interseptal segments more 

 convex on the outer than on the inner side ; its greatest width one 

 fifth that of the conch and twice as large as the septal perforations. 

 It is distant from the outer side by its own width in the apical 

 portion of the conch, but approaches the center in anterior 

 direction. The septal necks are short and curved outward assuring 

 thereby the position of this form among the Cyrtochoanites. The 

 interior of the siphuncle is filled with organic deposits, arranged in 

 vertical, radiating lamellae ; through its center passes a distinct 

 tubular endosiphotube with conchiolinous walls [see text fig. 55]. 



The shell is thick and the surface smooth. 



Position and locality. Professor Perkins, who collected the 

 type specimen, informs me that there is some doubt in regard to the 

 exact horizon and locality of the same. It was found in a lot of fos- 

 sils from the dove-colored limestone of Isle La Motte and presumably 

 comes from that horizon though the adhering matrix differs some- 

 what from that of the other specimens. We have observed 

 fragments of what we believe to be the same species in the 



