66 
DESCRIPTION OF SPECIES 
Endoceras sp. 
Plate XIV, figures 1A, B 
Conch enlarging at the rate of 10 or 11 mm. in a length of 100 mm., 
indicating an apical angle of 6 degrees. The specimen consists of part of a 
phragmacone 160 mm. in length and 56 mm. in width near the larger end 
of the specimen. Ten camerse occur in a length equal to the diameter 
of the conch at the top of the series of camerse being counted. 
Passing through the entire length of the specimen is a nearly 
cylindrical object, interpreted as the siphuncle, although its structural 
details cannot be determined. At the smaller end of the specimen the 
diameter of this siphuncle equals 0*42 of the diameter of the conch; at 
the larger end this ratio is 0*43; and about the same ratio is shown at 
mid-length of the specimen, where a transverse break discloses the siphuncle. 
At the smaller end of the specimen the siphuncle is almost in contact with 
the ventral wall of the phragmacone, but there is no downward flexure 
of the sutures along the median line of this ventral side indicating the close 
proximity of the siphuncle. At the upper end of the specimen that part 
of the outline of the siphuncle which is nearest the ventral wall of the 
phragmacone is not preserved, but an estimate, based on the curvature 
of that part of the transverse outline which remains, suggests that the 
upper end of the siphuncle is about 5 mm. from the ventral wall. In the 
absence of a vertical section, it is impossible to determine how far the 
septal funnels invaginate into the funnels next beneath. 
Locality and Horizon. From the southern part of the North arm, 
Great Slave lake; in the Ordovician. Collected by George S. Hume, 
Geological Survey, Canada. 
Remarks. The specimen of Endoceras here described probably is a 
new species, characterized by its rate of expansion and by the relatively 
low camerse. The latter are more numerous than in Endoceras angus- 
ticameratum Hall. They apparently agree in relative number with those 
of Endoceras duplicatum Hall, but the type of the latter species is much 
compressed. Owing to our meagre knowledge of the siphuncle, it is 
regarded as inadvisable to make this specimen the type of a new species. 
It is customary to differentiate Endoceras from Cameroceras chiefly 
on the basis of the structure of the siphuncle. Ruedemann 1 states the 
situation as follows. 
In Vaginoceras the septal necks extend beyond the next preceding 
septum, and the number of endosiphosheaths is great. 
In Endoceras the septal necks extend posteriorly only as far as the 
next septum, and the number of endosiphosheaths is smaller, and there 
is no internal lining within the siphuncle (endosipholining). 
In Cameroceras the septal necks extend to the preceding septum, 
there is an endosipholining, and there is one large, thick, walled sheath 
only in connexion with the living chamber. 
» Ruedemann, R.: New York State Mus., Bull. 90, p. 412 (1906). 
