ARCTIC ORDOVICIAN AND SILURIAN CEPHALOPODS 285 
specimen Id is unknown. In specimen le the siphuncle is 
submarginal in position; 5 camerae occupy a length equal to the 
diameter of the conch at the smaller end of the specimen, increas- 
ing to 5.5 camerae at the larger end; the surface of the shell is 
smooth. 
In specimen 1 on plate 17, the siphuncle is between 1 and 2 
mm. from the ventral wall of the conch; the surface of the shell 
appears to have been smooth; and, judging from the curvature 
of the small part preserved, the dorso-ventral diameter was 
distinctly shorter than the lateral one. In specimen lb, the 
siphuncle again is submarginal in- position. In specimen 2, 
the type of the variety distans, 4 camerae occur in a length equal 
to the diameter of the conch at the lower end of the specimen, 
increasing to 5 camerae in the second fifth of the length of the 
specimen above its base, to 5.5 camerae near mid-length, and 
to 6 camerae near its top; the siphuncle is within 1 or 2 mm. 
from the ventral wall of the conch. 
Specimens 2a and 2b on plate 58 were originally figured among 
Trenton species, although doubt was cast upon their occurrence 
in the Trenton. The matrix resembles that of typical Black 
River specimens from the Watertown area. Dr. Ruedemann 
states in a letter: 
I do not remember ever having seen an Actinoceras tenuifilum in the 
Trenton. It is quite common both in the Watertown and Leray lime- 
stones. Some specimens have been noticed in the Lowville (see Bull. 
145, New York State Mus., p. 841 footnote); Dr. Ulrich claimed at the 
time that these should be a different species, but none were collected. 
In specimen 2a mentioned above, the location of the siphuncle 
is submarginal, and the surface of the conch, as far as known, 
is smooth. In specimen 2b, the apical angle is 12 degrees. At 
the lower end of the specimen the diameter of the conch is 30 
mm. and that of the siphuncle is 19 mm.; at the upper end, 
the diameter of the conch is about 51 mm. laterally, that of the 
siphuncle being 26 mm.; judging from the curvature of the part 
preserved, the shell was slightly depressed dorso-ventrally. At 
the bottom of the specimen 6 camerae occupy a length equal to 
