AMERICAN PALEOZOIC CEPHALOPODS 
201 
transverse sections. In the other three species the siphuncles are 
relatively smaller and the camerae are closely crowded, as in 
Ellesmereoceras. It will require vertical sections of the types to 
determine their affinity with any confidence. 
The siphuncle of Orthoceras atticus, 0. becki and 0. explorator, 
all described by Billings from Canadian strata, is not in contact 
with the ventral wall of the conch, but is between the ventral 
wall and the center. The siphuncle of 0. atticiis was described 
by Billings as '‘not much, if at all, inflated between the septa.” 
That of 0. explorator is described as cylindrical. In none of the 
three species is the structure of the siphuncle known with suffi- 
cient accuracy to determine whether it belongs to the group with 
long septal necks, as in the Endoceroids, or to the group with 
short septal necks, as in the Orthoceroids. 
So far, no orthoconic cephalopods have been found in Canadian 
strata of which it is known with certainty that they belong to the 
Orthoceratida rather than to the Endoceratida. On this account 
it would be desirable to investigate all known Canadian ortho- 
conic species with the object of determining the structure of their 
siphuncles. It is evident that if typical Orthoceratida should 
prove absent in Canadian and Ozarkian strata, this fact would be 
of great service in identifying the horizon of some of the lower 
Paleozoic formations. 
The single specimen of Orthoceras primigenium, figured by 
HalT from the Canadian near Fort Plain in the Mohawk valley of 
New York, has a conch estimated to have been about 18 or 19 mm. 
in diameter at its lower end, enlarging possibly to 22 mm. at its 
upper end. A thickness of only 2 to 3 mm. of one side of the conch 
remains. There is no trace of annulation of the surface of the 
shell. The specimen consists of a living chamber 14 mm. in 
height above the suture of the uppermost septum. On the left 
margin of the specimen 12 camerae occur in a length of 9 mm. 
The two uppermost camerae are distinctly shallower than those 
beneath, suggesting that the conch had reached full maturity. 
The concavity of the septa along that part of the specimen which 
is preserved equals 2 mm. ; evidently toward the center of the 
original specimen this concavity must have been much greater. 
There the specimen in its present condition is 13 mm. in width, 
the maximum concavity is 4.5 mm. from the left side, and the 
’ Hall, J., Pal. New York, vol. 1, 1847, pi. 3, fig. 11. 
