OF THE RED CRAG. 



5 



the same species of Ziphius. There seems, however, to be another difference, if we may 

 judge from the figure of the upper surface of the cranium from Aresquiers, viz. the 

 continuation of a canal more or less unoccupied by the prefrontal (or so-called ' vomer') 

 along the upper part of the rostrum to its termination. The text of M. Gervais supplies 

 nothing to correct the plain inference from his figure. Moreover, the new and valuable 

 figures from the original type-skull of Ziphius cavirostris, in the Museum at the Jardin 

 des Plantes (pis. xxxviii, fig. 2, and pi. xxxix, fig. 1, Gervais, op. cit.), confirm the 

 accuracy of Cuvier's account of the proportion contributed to the rostrum by the pre- 

 frontal (fig. 1, 14' : 'vomer, h, " d'une singuliere epaisseur," Cuv., torn, cit., p. 351) ; whereas 

 the appearance of the homologous tract in the Z/'pMus from Aresquiers (Gervais, pi. xxxviii, 

 fig. 1) plainly shows it to form a narrower and less elevated tract at the upper part of the 

 rostrum. If this should signify something more than sexual or individual difference, I never- 

 theless concur with Prof. Gervais in rejecting its interpretation as a generic distinction. 



Returning to Cuvier's illustrations of his (supposed extinct) genus Ziphius, we find it, 

 next, illustrated by veritable fossils, from what is now known as the ' Middle Crag' at 

 Antwerp. Ziphius planirostris, Cuvier, is founded on specimens (figs. 2 and 3) which 

 include the rostrum, and so much of the expanded bases of the maxillaries and premaxil- 

 laries, with the palatines and pterygoids, as give the characters of the nasal passages 

 and base of the rostrum. The posterior part of 

 the basal or interorbital expansions of the maxillaries 

 and premaxillaries are, with the overarching nasals, 

 broken away. In the second of the two fossils in the 

 above general condition, to which Cuvier applied the 

 names Ziphius planirostris, he recognised and points 

 out differences which might be of specific value.i 



Regarding the first as the type of Cuvier's Ziphius 

 planirostris, its more perfect condition permits both 

 upper and lower apertures of the nasal passages to 

 be seen — a condition of value in appreciating the 

 generic osteological characters of Zijjhius. In the 

 upper view (fig. 2) the prefrontal (14) forms the 

 posterior wall and septum of the vertical respira- 

 tory canals, the septum being continued into a sud- 

 denly expanded tract (14'), which advances with an un- 

 symmetrical bend to the right, as in Ziphius Layardi^ 

 Plate I of th is Monograph . Any further definite tracing 

 of this mid-tract is not afforded by Cuvier's reduced 

 figure, beyond the canals [d, a) which terminate the pre- 



ie que le premier, ofFre des differences, qui pourroient passer pour 



Ziphius plan 



^ "L'autre morceau- 

 specifiques." — Op. cit., p. 



-plus 

 355. 



