OF THE RED CRAG. 



7 



the upper raid-tract of the rostrum shows a mesial linear groove, Cuvier attributes its 

 formation to the premaxillaries ; but in the previous species the anterior continuation of 

 the so-called ' vomer' is similarly grooved. The veritable premaxillaries are perforated at 

 their basal expansion, as in Zipluus planirostris, by the incisive foramina (marked d, d in the 

 illustrations of the present Monograph). The maxillaries, where, tracing them backwards, 

 they begin to expand, show the lateral ridge marked e, and the outlets of the suborbital 

 canal. On this fossil rostrum Cuvier founds his species Zljjliius longirostris. 



I now proceed to the inquiry, whether any existing species of Cetacea manifest 

 characters which can legitimately be interpreted as generically those of the Ziphius of 

 Cuvier, and whether they manifest corresponding modifications in the construction of 

 the rostrum with those interpreted by Cuvier as of specific value. 



I shall commence with the description of one of the series of Cetacean skulls transmitted 

 from the Cape of Good Hope, for description and comparison, to the British Museum. 

 Two figures of the instructive specimen in question have been published by my colleague 

 Dr. Gray, E.R.S. ; one is a copy of a drawing by Mr. Trimen, of Cape Town, under the name 

 Hyperoodon capensis ^ the other is an original woodcut from the specimen itself, as exem- 

 phfying the genus jPetrorhynchus, Gray.^ It would be an ill return for Mr. Layard's 

 liberal labour of transmission if the British Museum did not furnish him with such 

 anatomical accounts of his rarities as might serve or help to determine their genus and its 

 true affinities. 



Ziphius indicus. Van Beneden Petrorhynchus capensis, Gray ; (figs. 4, 5, 6, and 7). 



This species exhibits the interesting and instructive condition of a partial ossification 

 of the prefrontal or cranio-facial cartilage — so-called 'vomer' (fig. 4, 14, 14')- In this 

 skull the cranio-vertebral elements continued by or into that cartilage can be completely 

 traced. The prefrontals form, as usual, the posterior concave wall of the nasal passages, 

 where each is perforated by one larger foramen, for the trigeminal olfactory (?), and a few 

 smaller vascular foramina ; they coalesce at the mesial line, and rise as a low buttress- 

 like ridge abutting obliquely and unsymmetrically against the nasal bones ; the coalesced 

 parts then extend forward, as the thin ' septum narium,' with a sharp, free, superior concave 

 border ; the plate slightly thickens as it descends to be wedged into the vomer, expands 

 more as it advances in front of the nasal apertures, but subsides to the bottom of 

 the prenasal fossa, sinking almost to the level of the vomer, with which it has 

 coalesced, and there, at 14, shows a surface from 2 to 3 inches across and 9 inches 

 in length, concave both lengthwise and transversely, in which concavity was lodged the 



' ' Proc. Zool. Soc.,' April 11, 1865, p. 359. 



2 lb., June 27, 1865, p. 527. 



3 'Memoires couronnes et autres Memoires de rAcadcmie Royale de Belgique,' t. xvi, 1863. 



