Jackcl on Orthoccras. — Ruedcmann. 213 
considerably alter the conditions of static pressure of the orth- 
oceran shell. The calcareous siphonal excretions would then 
have hardly been intended to counterbalance the upward pull 
of the air-chambers and to furnish stability to the conch, they 
would rather appear to have increased the evil of pressure 
upon the apex. 
Of .special interest in this connection is the endoceratite, 
Nanno aulema Clarke, from the Trenton of Minnesota (Geol. 
Surv. Minn. v. 3, pt. 2; Pal. p. 770). This cephalopod had a 
wide proseptal siphonal cone, which is filled with solid lime- 
stone, a modification of the original organic deposit. This 
solid, heavy apical cone was "unquestionably," as Clarke as- 
serts, "external except so far as ensheathed by a mere coat- 
ing or film of the shell-tube." The chambered portion of the 
shell includes only a few relatively small chambers. This 
animal must have undoubtedly lived like the belemnites, and 
the apical cone must be functionally analogous to the rostrum 
of the latter. In regard to the belemnites it is claimed by 
Irlyatt and still more definitely by Jaekel, that they buried 
themiselves in the mud and used the rostrum as a post, "pax- 
illus," as Jaekel terms it, to secure themselves in the soft 
ground. We have then in Nanno an orthoceratite of which 
we can claim that it followed' the same praxis. This, how- 
ever, gives us a hint as to the use of the heavy deposits in the 
siphuncle of the other endoceratites, as well as of Actinoceras, 
Hormoceras and the groups of species of Orthoceras, occur- 
ring in the Devonic Schoharie grit of New York. The most 
typical of these Schoharie grit species, Orthoceras luxum, prav- 
um and oppletum frequently have their entire chambers solivlly 
filled with organic deposits as examination of the plates of the 
New York Paleontology, v. 5, pt. 2, (f. i. pi. 81) will readily 
show. It is a very suggestive fact that this Schoharie grit is 
a sediment consisting of quartz sand in a limestone matrix, 
which by its composition and encloised fauna indicates deposi- 
tion in the littoral zone and in disturbed waters. It seems prob- 
able that these orthoceratites used the weight of their shells 
to anchor themselves in the sand and thus prevent their being- 
torn from their moorings. But if those orthoceratites buried 
themselves in the ground, it is very probable that all the others 
did the same. 
