BEEKMANTOWN AND CHAZY FORMATIONS OF CHAM PLAIN BASIN 437 



Position and localities. We have seen two specimens from the 

 dove-colored limestone of Valcour island ; two from that of Isle 

 La Motte and two from the upper Chazy (C ) of the neighborhood 

 of Chazy village. 



Observations. This is the plainest cephalopod shell which we 

 have observed in the Chazy rocks of New York ; nor are we aware 

 of any other Chazy orthoceraconic form with which this one could 

 be confounded since its slow rate of growth and small siphuncle 

 serve to distinguish it from other small orthoceracones. It bears 

 however some similarity to O . recticameratu m Hall, a Low- 

 ville (Birdseye) limestone form from Watertown and the Mohawk 

 valley. In view of the fact that also some other Chazy fossils 

 continue into the Lowville and Black river limestones a closer com- 

 parison of the two forms became desirable. This has shown that O . 

 recticameratum is still somewhat more rapidly expanding, 

 has slightly deeper cameras (4 in 10 mm) and possesses somewhat 

 angular septa from which it derives its name. 



Genus geisonoceras Hyatt 

 Geisonoceras shumardi Billings (sp.) 



Plate 12, figure 4 



Orthoceras shumardi Billings. Can. Nat. & Geol. 1859. 4:460 



Original description. Elongate, cylindrical, section circular, 

 tapering at the rate of a little more than half a line to the inch, septa 

 rather strongly convex, distant nearly half the diameter; siphuncle 

 about one fifth the whole diameter, and with its center distant from 

 the center of the transverse section half its own diameter. Sur- 

 face unknown. 



In a specimen 8 inches long the diameter of the larger extremity 

 is 10 lines and of the smaller 5 lines and it tapers therefore at the 

 rate of ^8 of a line to the inch. At the larger end there are 2 septa 

 in 9 lines, and at the smaller 2 in 4 lines. The siphuncle is cylind- 

 rical and but slightly inflated between the septa ; its diameter at its 

 passage through the septum at the large end one line and a half, 

 and between the septa about two lines. 



We have no species with which this Orthoceratite can be com- 

 pared except O . amplicame.ratu m ( Hall) , from which it 

 differs in having the septa proportionally a little more distant, and 

 the siphuncle a little larger and not so excentric. 



Position and localities. The type specimen came from the Chazy 

 limestone of the Mingan islands. The specimen which we refer to 

 this species came from a Strephochetus bed of the middle Chazy 

 division B 2 at Chazy village. 



