436 



NEW YORK STATE MUSEUM 



in a shallow but open sea, the floor of which was studded with small 

 coral reefs. The excellent state of preservation of the two speci- 

 mens notwithstanding the thin shell and the fact that the larger and 

 coarser cephalopod shells in the same bed are frequently much 

 macerated, the rarity of the form and the long tubular shape in 

 combination with the bending of the conch would, however, indi- 

 cate that this species was burying itself or actively burrowing in 

 the mud. The central position of the siphuncle, the circular section 

 of the conch and the absence of any impressed zone indicate that 

 it is derived from some orthoceraconic form. As to its generic 

 position we have remained in doubt, but consider it as being closely 

 related, if not properly referable, to the genus Orthoceras s. str. 



O . ? vagura bears aside from its bending a considerable simi- 

 larity to O . s h u m a r d i Billings, a straight pencil-like form from 

 the Chazy of the Mingan islands from which 

 it can be distinguished by its considerably 

 . deeper cameras. 



sp. now 



Orthoceras modestum 



Plate 12, tig-lire 1-3 



Description. Small, slender orthoceracones 

 with circular section which judging from our 

 specimens may have attained a length of 130 



mm and a width of 15 mm. The rate of growth 

 is very small, about 1 mm in 30 mm. Frag- 

 ments of this stage of the conch appear pencil- 

 like, and in the ephebic stage the conch appears 

 to have become cylindric [see text fig. 14 and 

 pi. 12, fig. 2]. The cameras are moderately 

 deep, 5 cameras occupying the space of 10 mm 

 in the ephebic stage ; the septa are very shallow, 

 their concavity amounting to about half of the 

 depth of the cameras. The living chamber is 

 long (about 80 mm), hardly expanding and 

 provided with one or several constrictions; the 

 aperture is apparently straight transverse. The 

 siphuncle is small, a little more than 1 mm 

 wide, tubular, centren. The surface is marked with equal raised 

 transverse lines which are separated by equal interspaces and are 

 so fine that they can not be seen with the naked eye (11 in the space 

 of 1 mm). 



Fig. 14 Orthoceras 

 modestum sp. nov. 

 Natural section. Nat- 

 ural size 



