OF THE RED CRAG. 



35 



truin. The upper mesial margins of the premaxillaries, toward the end of the rostrum, rise 

 and converge above the prefrontal as in Zi.p/iius Layardi, to which the present species is 

 closely allied. The degree to which the end of the prefrontal subsides, the state of con- 

 fluence therewith of the premaxillaries, and the extent to which they are naturally or actually 

 apart at the end of the rostrum, can be determined only by inspection of the specimen 

 itself. The rostrum shows the usual ivory-like or petrosal hardness indicated by the 

 specific name.^ The under part of the rostrum is convex transversely, and part of the 

 vomer is there exposed. The antorbital foramen [e) is near the premaxillaries ; the entry 

 to the premaxillary canals {d) has the usual infundibular shape. Duvernoy approximates 

 Zip/iius lonprosfris, Cuv., to Mesodiodon densirosfris, because it shows a similar ossification 

 of the prefrontals (which he calls 'vomer') along the upper mid-line of the rostrum. 

 But we see, as in Ziphius indicus (fig. 8), that this condition may be associated with 

 a comparatively short and thick rostrum. 



The Mesoplodo7i of Gervais is the Mesodiodon of Duvernoy. I may add that, at 

 p. 60 of his Memoir (loe. cit.), Duvernoy cites, as one of the generic characters of 

 Mesodiodon — " Les intermaxillaires, elargis a la base du rostre ont le trou, en entonnoir 

 que distinguent les especes de ce genre but on this ground Clione ziphius must be trans- 

 ferred to Mesodiodon. In truth, however, the funnel-like expansion into which the 

 premaxillary foramina (</) open characterises, with a certain range of variety, the Ziphials 

 generally. 



Choneziphius, Duvernoy. — Of Cuvier's Ziphius planirosfris Duvernoy makes his 

 genus Choneziphius, acknowledging, however, that the premaxillaries " sont creuses d'une 

 cavite en forme d'entonnoir" (p. 61, as, indeed, Cuvier had expressly pointed out), 

 which character Duvernoy had previously made a distinction of the species of his genus 

 Mesodiodon, which includes, apparently, on that account, Cuvier's Ziphius longirostris. 



The dense petrous ossification of the mid upper tract of the rostrum, due to the 

 prefrontals, Duvernoy attributes to the 'premaxillaries' (p. 61), as in Ziphius longirostris 

 he ascribes it to the 'vomer' (p. 60). 



Placoziphius, Van Beneden.^ — This genus is represented by a fragment including the 

 base of a fossil rostrum discovered by Colonel Le Hon in an old deposit (' le crag noir" 

 or stage of the Neozoic series, at Edeghem, near Antwerp. In the breadth and superior 

 flatness of the preserved back part of the maxillaries this fossil resembles Ziphius planirosiris 

 and Z. planus. The prefrontal cartilage has not been ossified ; consequently there is, as in 

 Ziphius Sowerbii, fig. 13, and Z. Arnouxii, fig. 11, a vacant channel ("le canal vomerien," 

 V. Ben.) between the premaxillaries, the bottom of which canal is formed by the superior 

 vomerine groove. The expanded prenasal parts of the premaxillaries show the foramina 



' Originally imposed on it by De Blainville. 



2 Van Beneden, " Sur un Nouveau Genre de Ziphioide fossile (Placoziphius)," in ' Memoires de 

 i'Academle Royale des Sciences, &c., de Belgique,' tome xxxvii, 1866. 



