386 DR TRAQUAIR ON THE STRUCTURE AND AFFINITIES 
is sculptured with tolerably fine, irregular, angularly contorted, and interrupted 
rugee, with intervening furrows and pits, the pattern assuming sometimes 
almost a tubercular aspect. 
Along the posterior margin of the cranial shield are three plates (s. ¢, figs. 1 
and 2), one mesial, somewhat polygonal in form, and two lateral, each apparently 
of a triangular shape. These are obviously the representatives of the three 
plates, which occur in a similar position in Osteolepis, Glyptolemus, Megalichthys, 
&c., and of which different interpretations have been given by different authors. 
In Professor Huxtey’s description of Glyptolemus,* the mesial one is marked 
“ supra-occipital,” the two lateral, “ epiotic.” Mr Parxert has, however, pointed 
out that they are dermal bones, and not to be considered homologous with 
those other deeper ossifications of the cranial cartilage. By PANDER{ they are in 
Osteolepis simply designated ‘‘ Hautknochen,” and considered to be equivalent 
to the five little plates, which in the recent Polypterus occur immediately behind 
the transverse row of supra-temporals, and between the pair of upper supra- 
claviculars (supra-scapulars), being in reality the first scales of the back. On 
the other hand, he considered the transverse chain of small plates (supra- 
temporal) which lie immediately behind the parietals of Polypterus, to be 
represented in Osteolepis microlepidotus by the narrow portion of the cranial 
shield, which in that species is marked off near the hinder margin by a more or 
less interrupted superficial transverse groove. I am myself very much inclined 
to the belief that the three dermal bones in question are in reality equivalent 
to the transverse supra-temporal chain in Polypterus and Lepidosteus, and 
which have their representatives as well in the amphibian Labyrinthodonta as in 
most Teleostean fishes; the transverse grooving across the posterior part of the 
cranial shield in many Saurodipterines being probably only of the nature of 
superficial markings. 
Regarding the condition of the side walls, or of the base of the cranium, not 
the smallest information is yielded by any of the specimens. 
The facial bones in their general form and arrangement also remind us very 
much of those in both the “ Saurodipterini” and “ Glyptodipterini.” The gape 
extends very far back, so that the lower jaw is as long as the cranium proper, 
and the anterior margin of the operculum comes to be inclined obliquely down- 
wards and backwards. The operculum (op) is of a somewhat trapezoidal 
form, the anterior and inferior margins being the longest, the upper the 
shortest, while the posterior superior angle is obtuse and rounded. Below it © 
is in contact with the swboperculum (s. op), which is also trapezoidal, but not 
quite so large; its anterior superior angle is produced a little way upwards into 
a narrow sharp-pointed process overlapped by the operculum. In front of the 
* Dec. Geol. Survey, x. p. 2. + Shoulder Girdle and Sternum, p. 19. 
{ Ueber die Saurodipterinen, &c., des Devonischen Systems, St Petersburg, 1860, p. 11-12. 

