OSTEOLOGY OF RHAMPHOCOTTUS 465 



suture passing dorsally across the central part of the auditory 

 capsule to the inferior angle of the opisthotic; thence the suture 

 passes backward and inward below the pterotic and epiotic to 

 the median line, where a slight elevation marks the articulation 

 of the two exoccipitals, and which, with a sunilar elevation along 

 the middle line of the supraoccipital, forms a rather low supraoc- 

 cipital ridge (figs. 5 and 8). 



The supraoccipital (so.) is interposed posteriorly between the 

 upper posterior edges of the exoccipitals. Laterally it articu- 

 lates with the epiotics. Its anterior margin is obscured by the 

 parietals. 



The boundaries of the parietals (p.) could not be positively de- 

 termined in adult specimens. Laterally they enter into the com- 

 position of the strongly developed ridges which extend from the 

 prefrontals to the occipital spines. Dorsally they meet at their 

 posterior extremities (fig. 5). 



The epiotic (epo.) bone is somewhat pyramidal in form, the 

 apex of the pyramid being directed posteriorly (figs. 5 and 6). 

 This part of the bone is conspicuous in the entire specunen as a 

 long, strongly developed spine which is continuous anteriorly 

 with the supraorbital ridge. The posterolateral margin of the 

 bone articulates with the superior border of the posttemporal 

 (figs. 7 and 8). 



The pterotic (pto.) is irregularly triangular in outline. The 

 base of the triangle is produced laterally as a narrow ridge which 

 runs generally parallel with the occipital ridge. A minute canal 

 traverses this ridge, and ventrally, near the anterior end of the 

 bone, is a deep groove for articulation of the posterior part of the 

 head of the hyomandibular bone. Inferiorly the pterotic joins 

 the opisthotic by an irregular suture (fig. 5). 



The opisthotic (opo.) is a thin lamina of bone of rhombic form 

 situated on the side of the cranium between the pterotic above 

 and the exoccipital and prootic below (fig. 5). 



The prootic (pro.) consists of a thin lamina, which articulates 

 with the opisthotic and exoccipital bones superiorly and posteri- 

 orly, and a knob-like process near its anterior end which articu- 

 lates with a process of the sphenotic and the dorsal lunb of the 



