Parasphenoid of a Palceoniscoid. 



423 



Coming now to tlie posterior expanded part of the bone, 

 we find on the centre line of the specimen, and immediately 

 behind the posterior termination of the shaft and wings, a 

 distinct, rounded, slightly oval depression, Avhich is marked 

 out by a definite raised rim, broken in part by splintering of 

 the bone. Tiiis pituitary region — depression and rim — 

 is even better marked out iu the cast C of this dorsal 

 surface. 



By the side of the pituitary depression we have the right 

 anterior lateral process preserved, passing outwards and very 



Fig. 1. 



; Dorsal view of the compound para-basisphenoid bone of Rhadinichthys 

 monensis. (Specimen A.) X 7'0 diams. No. L 108:;0. M. M. 



slightly forwards. This process is apparently of the nature 

 of a thick flange of bone, constricted near the base, rounded 

 off at its outer and rather wider extremity, and bearing on 

 its dorsal surface two or three well-defined ridges. The 

 corresponding process of the left side is cut off by the broken 

 edge of the rock, whilst the posterior pair of processes is 

 also missing. 



A broad well-defined ridge runs outwards and backwards 

 on each side from the region of the pituitary depression, and 

 the whole of the expanded region of the bone posterior to 



