424 Mr. H. Day on the 



these ridges and the pituitary depression has the form of a 

 shallow basin-shaped hollow, with a circular outline poste- 

 riorly. The whole of this basin is floored by the actual 

 bony material, but for a few splinters flaked off on the 

 posterior margin. The surface of this hollow is almost 

 smooth, only a few faint radiating ridges and grooves being 

 visible. 



Immediately anterior to the broad ridge on each side, 

 mentioned above, there is a shallow depression, followed 

 anteriorly by a slight prominence. These appear as reversed 

 features on specimen C. 



Ventral View. (Specimen B.) 

 This specimen, as regards outline, is practically complete. 

 It exhibits anteriorly the long shaft described in specimen A, 

 and expands posteriorly as in that specimen. Both antero- 

 lateral processes are well preserved and will be described 

 below, and, in addition, we have also preserved in this case 

 the posterior pair of processes, which are of a wing-like 

 nature and extend outwards and backwards. 



The anterior shaft and its side-wings as described in 

 specimen A are here represented as cast, with the exception 

 of a small fragment of bone at the extreme anterior end of 

 the shaft. Hence, since the shape of the dorsal surface of 

 the shaft has been described as convex, the present specimen 

 simply exhibits the concavity in which it lay, and the side- 

 wings, which in dorsal view are concave, are represented as 

 convex surfaces. 



The posterior expanded part of the bone is extremely well 

 preserved, and gives us a ventral view of the bone whose 

 dorsal surface has been described in A. The portion pre- 

 served includes a short stump of the shaft, which is broken 

 off by a transverse fracture just in front of the posterior 

 termination of its side-wings. The shaft from this fracture 

 passes backwards and merges into a well-defined, raised, 

 diamond-shaped area, lying in the centre of the more or less 

 semicircular posterior expanded part of the bone. This 

 raised area must correspond with the shallow basin-shaped 

 area of the dorsal view. No trace is shown of a raised boss 

 corresponding to the depression for the pituitary body, seen 

 in dorsal view. There is, however, nothing extraordinary 

 in this, since, even in the common snake, the extremely 

 deep pituitary depression on the dorsal surface of the com- 

 pound para-basisphenoid is not represented in ventral view 

 by any boss or tubercle. Antero-laterally the diamond- 

 shaped raised central area is bordered on each side by a deep 



