532 MR. A S. WOODWARD ON [Dec. 7, 
the fact of its occurrence in more than a single type, leads to an 
interesting speculation, suggested to me by Professor Parker. Com- 
pared with the distinct anterior intertrabecular cartilage, which forms 
the axis of the rostrum in such primitive fishes as the glutinous 
Hags (Myzine)*, scarcely the slightest difference in form can be 
noted; and it seems not unlikely that we are here concerned with 
an admirable illustration of the principle, that the contours of super- 
ficial structures appended to the cranium are frequently determined, 
in the main, by the shape of the fundamental cartilages to which 
they are attached. The fossils, of course, do not permit a determi- 
nation of the complete form of the intertrabecular cartilage in any 
of these types, or of its primitive distinctness ; but the slight glimpses 
that can be obtained are rather favourable than otherwise to such a 
conclusion. 
Of the skin itself in Sgualoraja, only indefinite patches remain, 
and no small shagreen granules appear to have been developed in it ; 
but the sharp lateral edge, both of the rostral and caudal regions, is 
strengthened by a series ‘of minute calcified rings (fig. 1, d), evidently 
quite similar to those stiffening the boundaries of the snout in the 
living Pristiophoride. 
Cranium and Mandibular and Hyoid Arches.—Nearly all the large 
fossils under consideration reveal facts of more or less interest in 
regard to the structure of the skull; nos. I., 11., and IV., with 
Riley and Davies’s specimens, present the dorsal aspect, while no. III. 
and the fragment shown in Davies’s plate, fig. 4, afford some parti- 
eulars as to the conformation of the ventral surface. 
The palato-trabecular region (figs. 1, 2, pa.tr) extends far 
forwards in its present crushed condition, and from the centre is 
produced the long narrow intertrabecular cartilage (i.¢7) forming 
the axis of the snout. From each anterior outer angle of this region 
there also arises a more slender forwardly directed cartilage (pr. pa), 
which gradually tapers to an incurved point, as admirably shown in 
the left side of no. LV. (fig. 2). This prolongation evidently served 
to stiffen the edge of the base of the snout, exactly as its well-deve- 
loped homologue in the living Pristiophorus; and there can be 
little doubt that it:represents a definite prepalatine element, such 
as has not hitherto been recognized in the skulls of the Selachian 
order. Its form is almost identical with that of the corresponding 
cartilage in the Myxinoids, as will be at once seen on referring to 
Prof. Parker’s beautiful figures of Mywine and Bdellostoma®; in 
these fishes, indeed, the process serves a similar purpose, being like- 
wise placed to strengthen the sides of the rostrum. 
Immediately behind the origin of the prepalatine “ horns,” the 
lateral boundary of the palato-trabecular region gradually curves 
inwards for some distance, and then as slowly outwards again until 
it forms a well-marked antorbital prominence ; but the olfactory 
capsules, in their fossilized state, are totally unrecognizable, though 
1 W. K. Parker, ‘‘On the Skeleton of the Marsipobranch Fishes.—Part I. 
The Myxinoids,” Phil. Trans. 1883, pl. x. fig. 2. 
2 W. K. Parker, loc. cit, pl. x, figs. 1-3 and pl. xvii. figs. 1-3. 
