118 JIR. W. K. PARKER ON THE STRUCTURE AND 



found, will most probably differ from it iii one or otlier unimportant cliaracter, and yet 

 correspond with it in non-essentials. 



This is a short skull (Plate 23, figs. 5 and 6) ; the breadth is as to the length as 

 5 to 4, but the length is increased externally by the gi'eat retreat backwards of the 

 quadrate condyles ('/.<-■.), which make it, if measured by them, one-tenth more. 



It is also an extremely flat skull, and has a decurved snout ; it is very much unlike 

 the skuU of any of the " Eanidse" known to me, and the crania that answer to it best 

 are not yet described. I must therefore give an account of it as it is, and then refer 

 to it afterwards, when its image appears again in other types. The occipital condyles 

 {oc.c.) have large, oval, posterior faces, but they project very little and are separated 

 by a gentle emargination. 



With many deficiencies that make it lie some depth below the "norma," this skull is 

 ultra-Ranine in its general form, for it is extremely depressed, the otic regions are wide 

 wings, the jugal arch strongly bowed, and the hinge of the jaw is carried far behind 

 the occipital articulation. The skull is of full width in the temporal region ; then it 

 does not become narrower, but much broader, towards the antorbital region. The 

 margin above has a concave, and not a convex, outline ; the walls do not bulge, but 

 are scooped (fig. G). 



The dilated ethmoidal region is made still wider by superorbital expansions {so.h.), 

 and in front the whole nasal territory is but little narrower than the ethmoidal. Thus 

 the fore half of the cranium is in remarkable contrast with the hind half, and its 

 copious cartilaginous matrix is very similar to that which is seen in Skates and even 

 in the Cliimaera ; to make it still more archaic, the prenasal (p.«.) is a thick decurved 

 beak, such as is seen in an early stage of the embryos of many Vertebrata. 



The ossification of the occipito-auditory region is generalised, being continuous on 

 the same side {pr.o., e.o.) ; the synchondroses above and below {f.m.) are rather wide 

 and sub-equal. The fontauelle is quite covered ; it is single and lanceolate, with the 

 narrow end forwards ; the tegmen, beliind, is short; in front, it rather appears, than 

 is, extensive, for the ethmoid {eth.) is of gi-eat extent. The occipito-auditory bones 

 {'pr.o., CO.) nearly reach the fontanelle, under the roof-bones, above ; below, they touch, 

 over the parasphenoid, but leave the vestibular floor unossified. Above (fig. 5), the 

 bony matter leaves merely the tegmen tympani soft ; it is very narrow fore and aft. 



In front, below, the bony matter almost encloses the foramen ovale (V.), and fi'om 

 thence half the interorbital region is cartilaginous in this tract ; behind the middle of 

 it is the large oval optic fenestra (II.). 



The gii-dle-bone (eth.) occupies more than a tliird of the endocranium ; it borders 

 nearly a third of the fontanelle, and runs somewhat into the proper nasal territory. 

 Below (fig. 6), it affects the wings a little ; above (fig. 5), its edge is rounder ; it runs 

 quite clear of the superorbital " eave." A cross-shaped expansion, below, marks off the 

 shallow axils of this depressed bony mass ; these fossae are large, but shallow. The 

 cros!> is made more apparent by the extension forwards of the bony matter into the 



