AMERICAN PALEOZOIC CEPHALOPODS 
203 
fieldi Ruedemann.^ Orthoceras ordino.tu7n Billings likewise pos- 
sesses septal necks with concave vertical outlines within the 
camerae. In the three species here named the siphuncle is not in 
contact with the ventral wall of the conch. In all the other an- 
nulated orthoconic species described by Billings from Canadian 
strata, contact of the siphuncle with the ventral wall of the 
conch prevails. 
Nothing is known about the siphuncle of Orthoceras catulus, 
0. fiirtivum, and 0 . repens, beyond the fact that its general form 
is cylindrical, and that it is in contact with the ventral wall of the 
conch. All are Canadian species, described by Billings. 
In Orthoce7^as cataline, 0. xerxes, and 0. cato, also described by 
Billings from Canadian strata, the conchs are not only annulated 
but also striated transversely. In all three of these species 
the septal necks are distinctly concave within the camerae. Trans- 
verse striae were not discovered on any of the other Canadian 
annulated orthocones mentioned in the preceding paragraphs. 
In Orthoceras henrietta Dwight the conch is strongly annu- 
lated. The siphuncle is nearly in contact with the ventral wall 
and is 1 mm. in diameter where the diameter of the conch is 
6.4 mm. . 
Apparently all of the above species are to be included in Pro- 
to cy do ceims. 
5. ORYGOCERAS RUEDEMANN 
Genotype: Orthoceras cornuoryx Whitfield. Amer. Mus. Nat. Hist. Bull., 
1, 1886, p. 320, pi. 27, figs. 1, 2, 6; Ruedemann, New York State Mus. 
Bull., 90, 1906, p. 450, pi. 14, figs. 5-8, text fig. 19, 20 
Orygoceras is described as consisting of conchs which are 
smooth externally but which internally are annulated. The si- 
phuncle is small and is almost 1 mm. from the ventral wall of the 
conch. Ruedemann describes the siphuncle as orthochoanitic, the 
septal necks being short and straight and the remainder of the 
siphuncle being formed by the intervening connecting sheaths. 
In his figure,^® the vertical outline of the segments of the si- 
phuncle included within successive camerae is seen to have been 
concave. His section passes through the center of the siphuncle 
in a lateral direction. 
® Idem, p. 444, figs. 17a, b. 
Idem, p. 451. fig. 20. 
