bii2 MR. A s. WOODWARD ON [Dec. 7, 



the fact of its occurrence ia more than a single type, leads to an 

 interesting speculation, suggested to me by Professor Parker. Com- 

 pared with the distinct anterior intertrabeeular cartilage, which forms 

 the axis of the rostrum in such primitive fishes as the glutinous 

 Hags {Myxine) \ 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 intertrabeeular 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 Pristiophoridse. 



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. L, II., and IV., with 

 Riley and Davies's specimens, present the dorsal aspect, wbile no. III. 

 and the fragment shown in Davies's plate, fig. 4, afford some parti- 

 culars as to the conformation of the ventral surface. 



The palato-trabecular region (figs. I, 2, pa.ir) extends far 

 forwards in its present crushed condition, and from the centre is 

 produced the long narrow intertrabeeular cartilage (i.fr) 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. IV. (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 Pristiopkorus ; and there can be 

 little doubt that it represents a definite prepalatiue 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 Myxine 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-trabecnlar 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 fossihzed state, ate totally unrecognizable, though 



^ W. K. Parker, "On the Skeleton of the Marsip<ib-;inch Fislies. — Part I. 

 The Jlyxmoids.," Phil. Trans. 1883, pi. x. fig. 2. 



- W. K. Parker, loc. cit. pi. s. figs. 1-3 and pi. xvii. figs. 1-3. 



