Manchester Memoirs, Vol. Ix. (191 6), No. %. 45 



Glyptopomus, Osteolepis, and of the whole fish of Rhizo- 

 dopsis. These studies have shown that the Rhipidistian 

 skull is considerably more complicated than has previously 

 been supposed but that there is a great similarity amongst 

 all members of the group. We have described certain 

 new features connected with the fins which lead us to 

 conclude that the short type of paired fin found in Ens- 

 thenopteron is older than and has given rise to the biserial 

 " archipterygial " fin of Holoplychius. For the first time 

 we have been able to give a detailed description of the 

 feebly ossified hyomandibular of Rhizodopsis which recalls 

 the stapes of Eryops in being perforated by a foramen 

 near its proximal end. In the same fish we have been 

 able to describe certain features of the cartilaginous brain 

 case. In Rhizodopsis and Glyptopomus we have given an 

 account of the palate which considerably extends our 

 knowledge of the structure of this region,, and has a very 

 important bearing on the problem of Amphibian ancestry. 

 We describe for the first time the structure of the skull in 

 Phaneropleuron, and show that Dipterus valeuciennesi, 

 Dipierus platycephalus, Pentlandia macropterus, Scaumen- 

 acia> Phaneropleuron, Sageiiodus, and Ceratodus form a 

 phylogenetic series showing how Ceratodus is derived by 

 a process of specialisation and reduction from Dipterus. 

 Uronemus and Cteuodus are shown to belong to different 

 lines of descent, and the conclusion is reached that Dip- 

 terus valenciennesi is the most primitive as it is the oldest 

 known Dipnoan. Its skull is then compared with that of 

 a generalised Rhipidistian and the two are shown to agree 

 bone for bone the differences being entirely dependent on 

 the totally different adaptations of the two types. 



