ARCTIC ORDOVICIAN AND SILURIAN CEPHALOPODS 259 
writer has felt continually the necessity of bringing together 
from various sources all available material for purposes of direct 
comparison. In view of the extreme rarity of Arctic cephalopod 
material, especially from some of the horizons and localities 
studied by Dr. Holtedahl, the writer requested the loan of such 
cephalopods as were at hand, and to the kindness of Dr. Holte- 
dahl I owe the privilege of reexamining the material already 
once worked over by him. While the following pages do not 
add materially to the observations made by Dr. Holtedahl it is 
hoped they may be of some service owing to more detailed descrip- 
tion and additional illustrations of the cephalapods. 
As will be noticed in the following descriptions, most of the 
Arctic specimens here considered present sufficient detail to 
be of interest, and yet fall short of furnishing enough evidence 
for definite specific or, in a few cases, for generic reference. 
The lack of definite knowledge of the relation of the siphuncle 
to the cross-section of the conch in the Actinoceroids, and of 
the structure of the siphuncle in the supposed Cydendoceroids^ 
is especially unfortunate. What here is attempted is to secure 
all available evidence from such material as actually is at hand, 
in the hope that sooner or later it may lead to the securing of 
additional material. Such differences of opinion as here are 
expressed are made possible by lack of sufficient evidence, and 
evidently would disappear if more complete material could be 
secured. 
LIST OF SPECIES 
Gasteropoda, Canadian 
1. Cf. Euconia quebecensis Billings. 
Cephalopoda, Canadian 
2. Clarkoceras holtedahli Sp. nov. 
3. Eremoceras syphax (Billings) ; type. 
4. Ellesnierocei;^s scheii Gen. et Sp. nov. 
5. Protocycloceras lamarcki (Billings) ; types 
6. Protocycloceras whitfieldi Ruedemann . 
7. Protocycloceras cf. lamarcki (Billings) ; Bear island form. 
8. Deltoceras (?) sp. 
9. Kionoceras laqueatum (Hall) ; type. 
Black River and Trenton 
10. Kionoceras holtedahli Sp. nov. 
11. Kionoceras trentonense Sp. nov. 
