ARCTIC ORDOVICIAN AND SILURIAN CEPHALOPODS 297 
only 8 degrees, about 6.5 camerae occupy a length equal to the 
diameter of the conch, and the diameter of the siphuncle is 
about half of that of the conch. 
Under these conditions, Actinoceras tenuifilum is not considered 
as identical with Actinoceras higshyi nor with the Bear Island 
species here under consideration. How close the relationship of the 
Bear Island species is to Actinoceras higshyi can not be determined 
until a more exact knowledge of the type of the latter has been 
obtained. Judging from the greater apical angle of the Bear 
Island form, its more numerous camerae, and its relatively 
wider siphuncle, there is a probability of its proving distinct 
from typical Actinoceras higshyi. Its resemblance to Actino- 
ceras tenuifilum centrale is greater, but even in this case differen- 
ces may be noted and additional material will be required to 
determine the degree of relationship. 
24. Actinoceras parksi Sp. nov. 
Plate XXXV, fig. 3 
Actinoceras bigsbyi Parks, Trans. Royal Canadian Inst., 11, 
1915, p. 23, pi. 6, fig. 7. 
Type. — Specimen a fragment 140 mm. in length, consisting 
of one side of the phragmacone, exposing both the outer wall 
of the conch and the wall of the siphuncle. The conch enlarges 
at a rate of 18 mm. in a length of 100 mm. in a lateral direction, 
indicating an apical angle of 10° in that direction. The conch 
apparently is depressed in a dorso-ventral direction, but the 
depression appears to consist chiefly in a flattening of the median 
part of the ventral side. If this flattening is not due in part to 
compression during fossilization, then it must have formed a 
conspicuous feature of the original complete specimen. Possibly 
the dimensions at the larger end of the specimen were 68 mm. 
in a lateral direction and 52 mm. in a dorso-ventral one. At 
the smaller end of the specimen the corresponding dimensions 
appear to have been 48 and 44 mm. The rapid increase in the 
amount of flattening of the ventral side toward the upper end 
of this specimen appears to be too great to be normal, thus 
