220 B • 



a stout protuberance. This is at the inner end of a strong ridge, which dis- 

 appears near the outer edge of the pterotic. The protuberance looks as 

 though adapted for an articulation. The frontals send a process backward, 

 between the " supraoccipital " and the pterotic or postfrontal, to the base of 

 tlic tuberosity of the parietid. The suture between the exoccipital and pari- 

 etal is not clear. A suture is distinct enough, bounding the latter behind, 

 but whether an expansion of the supraoccipital intervenes or not is not 

 certain. The exoccipitals appear to be flat and quadrant-shaped, having 

 convex antero-lateral borders. Each bears a strong condyle. 



An isolated bone has the appearance of an ethmoid, or more probably a 

 vomer. It is cross-shaped, with the entering angles roofed by the contin- 

 uous margins, nearly flat on one side, and convex and rough on the otlier 

 C? superior) side. There are two parallel fossse on the under side of the 

 subconic apex, and four just behind the cross-arms (two external large, and 

 two median small). Tiiere are no teeth. 



The structure of the skull in this genus greatly elucidates that of the 

 Saurodonthlm, the cranium of an unknown species of which is figured on 

 Plate XLVII, figs. 7-8. It seems to possess the same composition poste- 

 riorly, but to be so extended horizontally as to render the identification of 

 the component parts much more easy. From a comparison of the two, it 

 appears that the bone supporting the crest on each side of the middle line is 

 the parietal, and as such bears an articular fticet lor the supratemporal. 

 That bearing the inferior facet of the same, becomes the epiotic. The 

 T-shaped bone of rachyrhizodus {Anogmius) is homologous with the ante- 

 rior basis of the median crest of the Saurodonlidce, which exhibits a section 

 of this form ; and we may suppose that this element in Pachyrhizodus does 

 not belong to the frontal bone, but to the supraoccipital. 



The rootless teeth, and, perhaps, the exoccipital condyles, separate this 

 Ibrm as a distinct family from the Saurodontidfe, while the exoccipital con- 

 dyles, and parieto-'foccipital articular facets, are not found in Eiic/iodu.s and 

 its allies. 



This genus was of less rapacious habits than the Sanrodontidie, and is 

 of less powerful construction. It was probably a bottom fish, with habits 

 s(nnething like those of Ba/rdcJitui, to which the known parts, especially the 

 teeth, bear some reseuddancc. 



