14 



BRITISH FOSSIL CETACEA 



dense, convex ridge (fig. 2, 14) an incli and a qnarter across at its broadest part, gradually 

 contracting to a breadth of half an inch when it has traversed one third of the length of 

 the rostrum. At about the terminal third of this part the outer margin of what seems 

 to be the suture between the prefrontal (14') and preraaxillary (22) rises and forms a free, 

 thin, inwardly or medially bent margin of bone, which soon appears as the upper and 

 outer border of a longitudinal canal, grooving the upper and medial surface of the 

 premaxillary, and gradually gaining vertical extent as it passes forward. The under and 

 inner margin of this groove is the, here, persistent medial suture or harmonia between the 

 prcmaxillarics, which suture becomes obliterated at about one fourth of the way backward 

 from the anterior end of the rostrum ; and, thus, any definition of the boundary between 

 prefrontals and premaxillaries becomes impossible. The solid terminal fourth of the 

 rostrum, in advance of the vomer (13, fig. 3, PI, I), is formed by the welded prefrontal 

 and premaxillaries ; behind this both bones, together with the vomer and the rostral parts 

 of the maxillary (ib., 21), combine to form the dense beak-like production of the upper 

 jaw, at the base of which are the palatines (ib., 20) and pterygoids (24). 



On the palatal surface of the rostrum (PI. I, fig. 3) the maxillo-premaxillary suture is 

 distinct, or linearly traceable, and the vomer (13) intervenes between the contiguous 

 palatal portions of the premaxillaries and maxillaries for an extent of one foot, gaining at 

 the middle of this extent a breadth of 8 lines, and having a smooth transversely convex 

 surface toward the palate. The degree in which the vomer thus appears upon the 

 bony palate exemplifies, with other characters, a specific difference in Zlphius as in 

 Belphinusy 



In Phoccsna brevirostris- and Euphysetes simus^ the limits of the prefrontals and of the 

 vomer can be defined ; the latter, in these and other Cetacea, is a long spout-shaped 

 bone, its canal looking upward, and this receives, posteriorly, the anterior coalesced parts 

 of the prefrontals, and, in advance thereof, the cartilage continued therefrom forward. 

 This cartilaginous prolongation of the ' septum narium,' formed by the coalesced portions 

 of the prefrontals, is ossified in the fossil kinds of Zlphius to be described, and projects 

 conspicuously between the premaxillaries at the upper surface of the rostrum, as it does 

 in Z. Layardi. 



In this species the ectomaxillary groove (PI. I, fig. 1, </•) commences posteriorly 

 between the antorbital plate of the maxillary (21') and the pterygoid (24')> and is continued 

 forward, diminishing in breadth and depth, upon the upper and outer border of the 

 maxillary to the fore end of the rostrum, or of so much as remains in the present specimen, 

 the extreme tip having been broken off. The lower boundary of the beginning of the 

 ectomaxillary groove formed by the pterygoid and maxillary extends outward as a thick 



' Compare, e.g., the skull of De/pA/nws (Stem) Gadamur with that of D. {Steno) frontatus ; or 

 the skull of Delphinus {Lagenorhynchus) fusiformis with that of B. {Lagenorhynchus) Pomegra. 

 2 Owen, "On Indian Cetacea," 'Trans. Zool. Soc.,' vol. vi, pi. ix. 

 2 Ibid., pi. xiii. 



