CEPHALOPODA. 783 
Actinoceras remotiseptum.] 
“The specimen described is a fragment which is worn through the center of 
the siphuncle. The proportions of this part of the fossil and the great distance of 
the septa contrast very strongly with the Ormoceras tenuifilum, and with other known 
species of the genus. 
“This species occurs in the higher part of the Trenton limestone, near Water- 
town, Jefferson county.” 
A large specimen from Cannon Falls, Minnesota, measuring upward of 300 mm. 
in length, much more complete than the original specimen of Ormoceras remotiseptum, 
has the dimensional characters of the latter, and upon sectioning a few of the air- 
chambers it shows a sipho in all respects like that of the type. The shell has been 
somewhat compressed, giving it a subelliptical cross-section where it was normally 
circular. 
The rate of expansion of the conch is very slow as shown by the fact that at 
the lower end the diameter is 46 mm., while at the upper end, the length of the 
specimen being 350 mm., the diameter is 70mm. The portion preserved retains 
no part of the body-chamber, and in this length of 350 mm. there are thirteen 
air-chambers, which increase considerably in depth from below upward, the first 
having a depth of 20 mm., the last of 83 mm. The sutures are normal and regular, 
possibly a little inclined towards the siphonal side, while the septa are deep and 
regularly convex. The sipho is large and submarginal. Atthe 7th septum, counting 
from below, the tranverse diameter of the sipho is 20 mm., that of the septum 58 
mm. In section it proves to be decidedly constricted at the septa and makes a 
broadly nummuliform expansion in the air-chambers, its diameter there being one- 
third greater than at the septa. It is very thick-walled and is penetrated vertically 
through the center by a narrow canal or endosiphon which gives off more or less 
irregular branches into the substance of the endosiphonal wall. In the relative depth 
of the air-chambers and the general form of the shell this species presents an 
external resemblance to Hall’s Orthoceras amplicameratum, from the Trenton lime- 
stone at Middleville, N. Y. In that species, however, the sipho appears to be small 
and suggests no relationship to Actinoceras. 
Formation and locality.—The single specimen observed is from the Trenton limestone at Cannon 
Falls, Minnesota. Collection of W. H. Scofield. 
Family ORTHOCERATID 4. 
Genus ORTHOCERAS, Breyn., 1732. 
The material representing this genus is measurably abundant, but not in very 
favorable condition for identification, and probably represents a greater number of 
