Parasphenoi'd of a Palceoniscoid. 



425 



valley whicli separates it from the anterior lateral process of 

 each side. This valley passes outwards and backwards on 

 the posterior flange-like side-process, where it flattens out 

 and disappears. 



Coming now to a consideration of the preserved part of 

 the shaft, we find that it exhibits a practically flat surface, 

 with posteriorly a "rather greater prominence, and possesses 

 numerous well-defined denticle-like prickles, best shown in 



Ventral view of the compound para-basisphenoid bone of 

 Rhadinkhthys sp. (Specimen B.) x 7'6 diams. No. L 10821. M. M. 



that part of the shaft immediately anterior to its posterior 

 diamond-shaped expansion. On this latter expansion there 

 is apparently a tendency for the prickles to fuse into longi- 

 tudinal, slightly diverging ridges. Numerous denticles also 

 occur in the antero-lateral valleys mentioned above, with 

 some slight tendency towards a linear arrangement. 



It now remains to consider the two pairs of lateral pro- 

 cesses. The anterior pair pass almost directly outwards, 



