210 BLKNNIID.E. 



tically situated, rather broader superiorly than inferiorly ; it has no 

 prominent ridges ; several foramina lead from the posterior margin 

 into the interior of the bone. The operculum is triangular, thin, 

 fragile, irregularly striated ; it tenninates in a stout and erect process 

 superiorly. Sub- and interoperculum narrow. In the mandihuJa only 

 the dentary and articular bones can be distinguished ; both are very 

 stout, entirely bony, and do not leave a free space between them. 

 The anterior portion of the former is armed with two strong, some- 

 what diverging canines, behind which are two smaller ones ; the 

 lateral portion bears exceedingly strong molar teeth, disposed in two 

 series on the middle of the bone and in a single one posteriorly. The 

 entire upper and lower margins of the mandible are formed by the 

 dentary, and the inferior branch has a distinct mucifcrous channel, 

 into which run four or five foramina. The outer surface of the 

 mandible is convex, whilst there is a deep triangular cavity on the 

 internal surface. 



We can distinguish three portions in the frontal bones : — The 

 interorbital portion is not quite three times as long as broad, flat 

 superiorly, but with many smaller and larger pores, a rather deep 

 groove between the orbits, and a pair of wide apertures at the an- 

 teiior extremity of the bones. The second (middle) portion is the 

 broadest, and distinguished by a large protuberance on each side, to 

 which the infraorbital ring is suspended. The posterior portion is 

 compressed to a sharp edge, which however does not project above 

 the level of the crown of the head. No bony ethmoid separates the 

 two orbits froiii each other. The infr-a orbital ring is complete, and 

 composed of five very irregularly-shaped boiies, the anterior of which 

 is the largest and the posterior the smallest. 



The basisphenoid is extremely large and broad, and is compressed 

 into a sharp inferior edge. The alisjjhenoid is subquadrangular, with 

 several low ridge's radiating from the foramen, through which the 

 nerves pass. The postfrontal is vertically situated, and distinguished 

 by a sharp prominent crest above the articular caA^ty for the tym- 

 panic bones. The mastoid is immediately behind the postfrontal ; 

 it extends upwards to the crest -of the frontal bones, forms another 

 crest together with the parietal on each side of the occiput, and a 

 very deep conical cavity together with the parietal and paroccipital. 

 The parietal is one of the smaller bones of the head, and forms a part 

 of the posterior region of the skull, which is slightly impressed and 

 descends obliquely backwards. 



The occipital bones are very distinctly separated from each other. 

 The interior of the basioccipital ajipears tcT be very porous. The 

 exoccipitals are, as usual, provided with a joint for the first ver- 

 tebra. The paroccipital is laterally produced into a large prominence ; 

 and the supraoccipital has a slight longitudinal crest. 



The vertebral column is composed of twenty-six abdominal and 

 forty-nine or fifty caudal vertebra;, the length of the former portion 

 being to that of the latter as 1 : 1-7. The first vertebra is very com- 

 pressed, like a disk ; the neural and lucmal spines are well deve- 

 loped, and the latter of the first caudal vertebra form a complete ring. 



