NIAGARA GROUP. 
293 
660. 37, ORTHOCERAS UNDULATUM. 
Pl. LXIV. Fig. 1 a-f; and Pl. LXV. Fig. 3. 
Compare Orthoceras annulatum, Sowerby, Min. Conchology, Vol. ii, 1318, p. 77, t. 133. 
“ — — Hisinger, Anteckn. v, lab. iv, fig. 6. 
“ — — Id. Vet. Acad. Handl. 1826, t. vii, fig. 8. 
“ — — Id. Petref. Suecica, 1837, p. 28, t. x, f. 2. 
Not O. undulatum, Sowerby. 
“ O . defrancii, Troost. 
Cylindrical, very gradually tapering ; siphuncle subcentral; annulated by strong rounded 
annulations, which are distant from each other one-fourth to one-fifth the diameter; surface of 
the shell marked by undulating and more or less imbricating laminae. 
In a single imperfect specimen, where the siphuncle is visible, it appears to be a little 
eccentric, but this appearance may be due to pressure. The specimens obtained have been 
usually in the soft shale, and completely flattened, so that septa and siphuncle are obliterated. 
The shell is frequently more or less abraded or dissolved, and the characters of the surface 
are variable. Sometimes the shell is entirely removed, and the annulations alone mark the sur¬ 
face. A comparison with Swedish specimens leaves no doubt of the identity of our species with 
0. undulatum of Hisinger ; and the figures in Murchison’s Sil. System, from the Wenlock 
formation, are evidently identical with ours. It is extremely doubtful, however, if 0. annulatum 
of Min. Conchology is the same species, particularly since all the evidence we have of its 
geological position would go to show that it belongs to a later period, and we have in our 
s uccessive formations several annulated species of Orthoceratites which are not very unlike that 
one. Under these circumstances I prefer to adopt the name of Hisinger, until it be demonstrated 
that the two 0e identical, when the name given by Mr. Sowerby will have precedence. 
Fig. 1 a. A fragment of this species on a slab of shale : the sharpness of the laminae has been 
much reduced either by maceration or solution. 
Fig. 1 b. Another fragment where the laminae are nearly obsolete. 
Fig. 1 c. A fragment replaced by gypsum, and preserving only the annulations. The substitution 
of the sulphate of lime has doubtless taken place from the solution of the original 
shell and the calcareous interior, and we have merely a cast preserved. 
Fig. 1 d. A fragment near the smaller extremity, showing the laminae but partially preserved. 
The very gradual diminution shows the species to have been extremely elongated; 
and I have seen fragments of a single individual, more than two feet in length, and 
imperfect at both extremities. 
Fig. 1 e. Transverse section of an imperfect and somewhat distorted specimen, showing the 
position of the siphuncle. 
Fig. 1 /. Vertical section showing the convexity of a septum. 
Plate lxv, fig. 3. A fragment of this species from near the aperture. The shell is nearly all re¬ 
moved by maceration, and the interior is mostly covered by the little coral Sagenella. 
