ON MEGALICHTHYS 325 



Part III. 



The Systematic Position and the Relationships 

 of the Genus. 



A comparison of Megalichthys with other members of the 

 Rhipidistia is almost sufficient in itself to convince one that 

 the classification of these genera into groups of family rank 

 is premature ; it is evident that much must be added to our 

 knowledge of some of the genera before the data be adequate 

 to enable us to work out their exact relationships to other 

 members of the group. 



In many respects the similarities between Megalichthys of 

 the family Osteolepidae and Rhizodopsis of the family 

 Rhizodontidas are greater than those which unite Megalichthys 

 to Osteolepis, the type genus of its family. This is sufficient 

 to shew the insecurity of the position which Megalichthys holds 

 among the Osteolepidae. In all three genera the shape of the 

 body is very much the same, and the features which are 

 stressed in the distinction between the two families are the 

 scales and the folding of the walls of the teeth. The latter 

 character is, in this case, one of much less than family 

 significance, since it concerns merely the degree of folding. 

 In the Rhizodontidas there are vertical infoldings, but they are 

 comparatively few and simple, and in Rhizodopsis itself the 

 teeth are described as round in section, and smooth. In 

 Megalichthys hibberti the teeth have fine superficial vertical 

 striae at the base, where they are folded, and they are smooth 

 above. Megalichthys agrees with Rhizodopsis in having the 

 parietal region longer than the fronto-ethmoidal. In Osteolepis 

 the length of the parietal shield of the type species is only 

 two-thirds that of the fronto-ethmoidal region. 



Megalichthys differs from both Rhizodopsis and Osteolepis in 

 the fact that synosteosis has not generally taken place between 

 the frontals and the compound ethmoidal shield, and also in 

 the fact of having three instead of two nuchal plates. 



Megalichthys and Rhizodopsis are both without the median 

 (pineal) foramen ; but this feature is present not only in 



