1871.] Dr. A. Giinther's Description of Ceratodus. 379 



are also a pair of narrow oviducts, with or without a narrow peritoneal 

 opening, each confluent with the ureter of its side. 

 In the concluding chapters it is shown : — 



1. That Ceratodus and Lepidosiren (Protopterus) are more nearly allied 

 to each other than to any third living fish, that they are well-marked 

 modifications of the same (Dipnoous) type, the latter genus diverging 

 more towards the Amphibians than the former. 



2. That the difference in the arrangement of the valves of the bulbus 

 arteriosus cannot longer be considered of sufficient importance to distin- 

 guish the Dipnoi as a subclass from the Ganoidei ; but that the Dipnoi 

 may be retained as a suborder of Ganoidei. 



3. That the suborder Dipnoi may be characterized as Ganoids with the 

 nostrils within the mouth, with paddles supported by an axial skeleton, 

 with lungs and gills and notochordal skeleton, and without branchio- 

 stegals. 



4. That a comparison of Teleostei, Chondropterygii, and Ganoidei shows 

 that the two latter divisions, hitherto regarded as subclasses, are much 

 more nearly allied to each other than to the Teleostei, which were deve- 

 loped in much more recent epochs; and therefore that they should be 

 united into one subclass — Palceichthyes — characterized thus : heart with 

 a contractile bulbus arteriosus ; intestine with a spiral valve ; optic nerves 

 non-decussating. 



5. That there is very strong evidence that the suborder Dipnoi was re- 

 presented in the Devonian and Carboniferous epochs by the genus Dipterus 

 (? = Gtenodus) ; but that, although Dipterus has internal nostrils and even 

 a pair of vomerine teeth (beside the molars) like the living Dipnoi, it must 

 be placed as the type of a separate family of this suborder, on account of 

 its heterocercy. 



6. That the evidence with regard of Phaneropleuron (Huxley) is less 

 conclusive ; and that Tristichopterus (Egerton), with the complete segmen- 

 tation of its vertebral column, must be excluded from this suborder. 



7. That the suborder Crossopterygii (Huxley) contains two distinct types 

 of " lobate fin," viz. the " obtusely lobate," with a transverse series of 

 carpal cartilages, and the " acutely lobate " with an axial skeleton. Only 

 the latter type agrees with the structure of the Dipnoous limb. But 

 Polypterus, Coelacanthus, &c, which are provided with fins of the former 

 type, are genera sufficiently distinguished also by other characters, to be 

 placed into a separate suborder. 



