554 PROF. W. B. BEXIIAM AND Mil. W. J. DITNBAK ON [May 15, 



prominence as it does in li. ghsne, it barely readies the groove 

 (PI. XXXIX. fig. 4). 



Preorhltal Region. 



In front of the orbit is the prenasal " beak," a solid structure 

 composed pai-tly of bone and partly of cartilage. It is compressed 

 from side to side, with a shai-p dorsal and ventral edge. The 

 greater part of the beak is formed by the mesetlunoid," wliich is 

 mainly cartilaginous, and by the ectethmoiil cartilage. The 

 Mesethmold is, as its names implies, a mediaii sheet "extending 

 from the orbit half way to the anterior extremity of the "beak," 

 whei-e it meets another vertical plate, a part of the vomer. Its 

 posterior end is laterally broadened and appears on the roof of 

 the oi'bit, of which it forms the anterior median wall. 



The Ectethmoiil cartilage is a thick mass of cartilage (without 

 aiiy ossification, such as occurs in B. glestie) extending outwards 

 at light angles to and continuous with tlie mesethmoid, forming 

 a rounded prominence, the anterior boundary of tlie orbit. The 

 lower mai'gin of the prenasal rostrum is formed by the vooner. 

 This bone tapers from its middle to each end ; the anterior end 

 curves sharply down to form a median tooth, and on each side of 

 this are two smaller lateral teeth*. Of this thei-e is no mention 

 in the description of B. glesne. The posterior end of the bone 

 meets the parasphenoid. As mentioned above, the vomer sends 

 a vertical plate up\\'a.rds to meet the mesethmoid by its posterior 

 margin. Above this vei-tical sheet is a stidp of cai'tilage — the 

 prenasal cartilage — extending back over the mesethmoid" to the 

 " tegmen cranii " and forming the dorsal edge of the " beak." 

 Behind the vomer, the Parasphenoid foi-ms at least two-thii'ds of 

 the ventral mai'gin of the skull. It is sword-shaped, the pos- 

 terior region or ''handle" having two Literal projections — the 

 "guards" — near this end. These slope outwards and very slightly 

 backwai'ds and shai-ply upwards to meet the sphenotics. In 

 R. glesne the parasphenoid is greatly extended backwards and 

 upwards as a vertical plate undeilying and extending behind the 

 basioccipital. In the present species there is, howevei-, no trace 

 of such a plate, and the posterior end of tlie bone tapers to a 

 point which lies well in fi'ont of the hinder end of the basi- 

 occipital. 



Lying in front of the orbit, close under the skin, are the nasals 

 and'preorbitals (PI. XXXVIII. fig. 1). The Nascd is a small 

 rod-like bone which articulates with the anterior end of the frontal 

 and, passing forwards and inwards, abuts loosely against the sides 

 of the premaxilla. Under the nasal lie the rreorbiials, two on 

 each side. These thi'ee bones readily separate fiom the skull and 

 ai'e shown only in figure 1. 



* The fact tliat this youns: specimen is pi-ovided vvitli teeth in botli the npiier 

 and lower jaw is sug£.estive ; for in some of the siiecimeus of R. (/leme that have been 

 described they are present (cide Luiuthei'), in others absent (I'idc Parker). 



