776 THE PALEONTOLOGY OF MINNESOTA. 
([Cameroceras. 
retrally directed funnels of the septa. This is well illustrated by a very large and 
essentially entire internal cast of the sipho, measuring 5 feet 3 inches in length, a 
reduced drawing of which is shown on plate xtvu. The principal extent of the 
surface of this specimen bears traces of the contiguous or overlapping septal funnels 
which have thus created a discontinuous siphonal tube. The specimen is so drawn 
as to show the side nearest the margin of the conch; hence the remnants of the septa 
show a marked angularity due to their concavity. Thisisa trait characterizing all such 
siphonal casts in which the position of the sipho was lateral. With variation in 
the position of the sipho and in the concavity or obliquity of the septa, these siphonal 
funnels vary in their direction. It will be observed that at a short distance from 
the apex of this cast is an abrupt contraction in its diameter, which is continued to 
the apex. This apical portion is the internal filling of the solid and continuous sheath 
whose probable extent and thickness is indicated by a dotted line which carries the 
sipho to an apex according to the slope of the discontinuous sheath. The evidence 
afforded by this specimen is abundantly fortified by others which demonstrate that 
this solid apical portion of the sipho is but a filling and thickening of the vacated 
and discarded apical cavity of the otherwise discontinuous sheath. 
The internal casts of this long apical cone are of far more frequent occurrence 
than those of the funnel-tube, because the parts of the latter are not often coherent 
and usually the latter are found to retain the overlapping or approximate parts of 
the septa upon their surface. 
The great siphones of the dead shells of these creatures afforded favorite retreats 
for other and smaller cephalopods, and they are hence frequently found crowded 
with diverse species of Orthoceras and Cyrtoceras, sometimes three or four being 
crowded in side by side, or one within another, in such cavities. 
The material examined does not afford the most satisfactory evidence of the 
duplication of the siphonal sheath, and it would seem that much of the evidence that 
has been adduced in regard to the presence of such duplicate sheaths requires 
re-examination, although it is by no means intended by this expression to cast doubt 
upon their existence. In some accounts of these fossils a careful distinction between 
the apical sheath, its filling, and such adventitious or hermit orthocerans as may 
have got in, has not always been made. Attention may be directed to the internal 
siphonal cast shown on plate 1, fig. 3, which shows a portion of the filling of the 
discontinuous part of the tube and an acuminate terminal process which indicates 
a tubular cavity near the apex of the solid sheath. Whether or not this ever 
penetrated the solid sheath and thus represents a true endosiphon communicating 
with some other sheath, as in Piloceras, cannot be determined from such casts. 
