202 The American Geologist. Apni, 1903. 
"c) The shell not only frequently shows a pronounced 
transverse sculpture, but it may even be provided with ring- 
like swellings (annulate forms). Both phenomena are irrecon- 
cilable with a rostral function of the shell, as both would offer 
friction and resistance to the water pressure. 
"d) The strictly symmetrical form of the shell contrasts 
sharply with the shells of the squids, nor does it, aside from 
its heaviness, find an analog in the shell form of the pteropods, 
which also fail to display any such pronounced monaxial bi- 
lateral symmetry. 
"e) The straight truncation of the ostial margin, together 
with the symmetrical form of the whole shell, excludes also 
the possibility that the orthoceratites were crawlers bearing 
their shells on their backs after the fashion of snails. 
"On the other hand, the following facts argue, in my opin- 
ion, for the sessility of the ortJwceratites : 
"a) The radially symmetric structure, which everywhere 
in the animal kingdom is characteristic of sessile forms, ap- 
pears in the circular section, the straight truncation of the 
aperture of typical orthoceratites, the position of the threi or 
five submarginal impressions in the living- chamber, the regu- 
lar growth in thickness and an occasional regular, radially 
symmetric arrangement of longitudinal ridges upon the sur- 
face, and can be readily explained only by conditions of static 
pressure during growth. 
"b) The shell is usually broken off at its lower end; which 
is an exceptional condition in externally similar gastropod shells 
such as Fusus, Turritella, Terebra or in the very slender shells 
of pteropods. Among the thousands of observed orthocera- 
cones initial chambers have become known in but a few forms. 
The apex is hence nearly always broken, a fact which indicates 
that it was held by an external force after the death of the 
animal. In those cases where the apex has been observed in 
well preserved state, it shows a scar which, like that at the 
first air chamber of the ammonites, apparently permitted to the 
sipho a connection with the contents of a protoconch as yet 
unknown. 
"c) The agreement of the shell structure of the orthoce- 
ratites with the conularias seems to me unmistakable. The 
latter show a radially symmetric structure ; with them a trans- 
