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1930] Romer, The Pennsylvanian Tetrapods of Linton, Ohio
115
Stegops is known almost entirely from the two skulls which are the
types of the species given above. That of Stegops divaricata is practically
complete, and exhibits a nearly perfect skull roof, together with rpuch of
the palate, although the under surface is partially obscured by the jaws
which lay along its lateral margins. The type of "E. tuberculatus"
showed little in its original condition, but upon development reveals the
greater part of both suifaces of a similar skull, with some postcranial
material.
As seen from above, the skull is comparatively short and broad, with the orbits
about in the middle of the length and placed far apart. The most striking feature is
the presence of "horns" in the tabular region, while other projections are found more
medially. The ornamentation consists of a group of rounded tubercles in the center
of each element, and radiating from them a series of nearly straight ridges, the most
prominent of which are usually in groups of three or more, running parallel to one
another towards the centers of ossification of the adjacent elements.
What appear to be the lateral line canals appear as a set of rounded much raised
ridges, which, as far as I have seen them, run forward from the "horns" along the
outer side of the tabulars and reach the posterior margin of the orbits on the postorbital.
From here they form a ring entirely surrounding the orbits. Anteriorly two
ridges extend the system forward, one traversing the prefrontal to pass forward along
the length of the nasal and loop backward on the premaxilla anterior to the external
naris; the second ridge turns down over the lacrymal and presumably turned forward
on the maxilla to join the ridge just described. There are apparently fine pores on the
surface of these ridges, while the ventral surface of the bone is also elevated, suggesting
the presence of a tubular "canal" beneath the roofing bones.
The elements of the median row of roofing bones are all remarkable for their
breadth; especially noticeable is the large size of the nasals, and the shortness of the
parietals. The lacrymal is short and is excluded from the naris by a contact between
maxilla and nasal. The postfrontal is large, but both the postorbital and jugal are
comparatively small, although the former has a long posterior process carrying one
of the lateral line ridges. There is but one large element, in which I can detect no
suture in the usual position of the tabular and supratemporal.
The sides of the skulls are imperfect in the temporal region, but the squamosal
seems to have been rather small, and the quadratojugal comparatively large, with
some evidence of spinescence on this last element.
The teeth in both jaws are numerous, and rather stout and bluntly conical.
On the palatal surface, one is immediately struck with the very large size of the
interpterygoid vacuities and the large prevomers. A chagreen of small teeth covers
practically all the exposed surface of the prevomers, vomers and ectopterygoids
and pterygoids and most of the exposed surface of the parasphenoid and the ventral
surface of the braincase as well. As in Erpetosaurus, there are indications of small
ossifications bearing these small teeth which lay in the roof of the mouth in the interpterygoid
vacuities. The thenar teeth on the prevomers and pterygoids are in their
usual position, but are of very small size ( I have not seen those which may have
been present on the ectopterygoids). The prevomers, as noted above, are extremely
large, have a broad contact anteriorly with the premaxille, and form most of the