EEEKMANTOWN AND CHAZY FORMATIONS OF CHAMPLAIN BASIN 435 



Orthoceras (?) vagum sp. nov. 



Plate 13, figure 1-3; plate g, figure 9 



Description. Very slender gently and irregularly bending conch, 

 attaining a length of 250-I- mm and a width of more than 20 mm. 

 Its rate of growth is but 3 mm in the space of 50 mm ; its section 

 circular. The cameras are relatively deep, there being five in the 

 space of 20 mm where the width of the conch is 13 mm, and four 

 in the same space where it is 18 mm. The septa are strongly convex, 

 their depth being nearly equal to that of the cameras. The sutures 

 pass straight transversely. Length of living chamber and char- 

 acter of aperture have not been observed. The siphuncle is centren, 

 slightly nummuloidal, one fourth the width of the conch, and ap- 

 pears to have remained empty. The shell is thin, its surface smooth 

 or only marked with faint transverse growth lines. 



Position and localities. Two specimens of this type have come to 

 our notice; one of these is from the dove-colored limestone of Val- 

 cour island [collected by Prof. G. H. Hudson] ; the other [in the 

 American Museum of Natural History] is from the same horizon 

 of Isle La Motte in Lake Champlain [coll. by Prof. H. M. Seely]. 



Observations. The most striking character of this species is the 

 irregular bending of the conch. This is but slightly though dis- 

 tinctly shown in the specimen from Isle La Motte, a photograph of 

 which has been kindly taken for me by Dr Hovey [pi. 13, fig. 3]. 

 In the other specimen from Valcour island, which I have been able 

 to free entirely from the rock, the bending is very obvious and 

 clearly not caused by fractures or folding in the rock for it takes 

 place in different planes [see fig. 2], is nowhere abrupt and the 

 septa are arranged slightly closer on the inner side of the curves 

 than on the outer, exactly as in the regularly curved phragmocones 

 of Cyrtoceras etc. Nor do the orthoceracones associated with this 

 species in the same bed or (as in the Amer. Mus. specimen) even on 

 the same slab show any trace of secondary bending with the in- 

 cluding matrix. 



Speculations as to the cause of this peculiar aberrancy naturally 

 urge themselves upon the observer of the irregular orthoceracone. 

 The assumption that weakening physical conditions of the environ- 

 ment, such as are found in the lagoon of a coral reef affecting the 

 regularity of the volutions of gastropods might have produced this 

 form, seems to be refuted by the character of the associated fauna 

 which is largely one of straight gigantic cephalopods and stromatop- 

 oroid corals, suggesting that the dove-colored limestone was formed 



