OF THE RED CRAG. 



15 



convex buttress (e), some way beyond the upper boundary, subsiding, as it advances, at 

 about the basal fourth of the rostrum. At about the middle of the rostrum the lower 

 border of the ectomaxillary groove again projects, but as a sharp, somewhat jagged ridge; 

 at the anterior third of the rostrum the upper part of the groove similarly projects, the 

 lower one having subsided ; such ridge or ridges I indicate as ' ectomaxillary,' but they 

 evidently represent anteriorly the alveolar groove of toothed Delphinidce. The interorbital 

 plate of the maxillary is perforated by the two large apertures («, h) for the transmission of 

 nerves and vessels, answering to those marked « and ^ in PI. IX {Phoccena brevirostris) , 

 PI. XIII {Euphjsetes sivius) of my Memoir, above cited, on Indian Cetacea, homologous 

 with the suborbital or antorbital division of the fifth nerve in land mammals. The fore 

 part of the nasal processes of the premaxillary are also perforated by a smaller canal, 

 whence a groove is continued some way forward along with the suture between the nasal 

 plate of the premaxillary and the medial (prefrontal) part. 



The outlets of the bony nostrils (PI. I, fig. 2, /, r) are slightly twisted from behind 

 forward and to the right, the right outlet (?•) being the widest ; the intervening septum 

 shows a corresponding departure from symmetry. The posterior part of the premaxillaries 

 (ib., fig. 2, 22) diverge, expand, and rise to define the cavity around the nostrils, or 'prenasal 

 fossa,' as in all Z'qjJiii. 



The pterygoid is a broad, vertically extended, triangular plate of bone, widely and 

 rather deeply excavated in the major part of its extent (fig. 1, 24'), the non-excavated 

 anterior apex (2 4) being wedged between the maxillary and palatine at the lower and outer part 

 of the base of the rostrum. The inferior thin border of the excavated part is slightly everted, 

 and is applied to the corresponding part of the opposite pterygoid, leaving a deep fissure 

 intervening and contracting posteriorly (ib., fig. 3, 24'')- The breadth and depth of this 

 ' interpterygoid fissure' varies in the species of ZipJdus} The conchoidal part of the 

 petrotympanic is bilobed posteriorly, but less deeply indented than in Belphinus ; it is 

 rather widely open or unfolded anteriorly, with a thin, compact, involuted wall ; the petrosal 

 part articulates by a posterior process to the mastoid. 



Being unable to draw the line of generic distinction at any of the gradations of length 

 and slenderness of snout occupying, in this respect, the interval between ZipJdus indicus, 

 figs. 4 — 7, and Zipldus Layardi, PI. I, and meeting the same difficulty in the degrees in 

 which the prefrontal cartilage of the rostrum becomes ossified, I hold by the well-defined 

 characters of the Cuvierian genus ; and, premising the above definitions of recognisable 

 parts of the Ziphial rostrum, I proceed to apply them to the specific definition of the 

 petrified snouts from the 'Red Crag.' 



1 It is wide, e. g. in Ziphius patachonicus, pi. xvii, fig. 2, h h, of Burmeister, ' Anales del Museo publico 

 de Buenos Ayres,' 4to, 1868. 



