4 Dr. K. II. Traquair on the Genus Dipterus. 



sion of this ])oint must be reserved for a more suitable occa- 

 sion. I liave seen no S])ecimens of Ctenodus which throw 

 light upon the question." However, a little furtlier on he 

 says again, '' It is not known whether Dl-pterus and Ctenodus 

 are hyostylic or autostylic ; but Polypterus is hyostylic. It is 

 not known whether Dipterus and Ctenodus have an archi- 

 pterygium or an ichthyopterygium ; but the outward resem- 

 blance of tlie fins of Dipterus to those of Ceratodus renders it 

 probable that they have an archipterygium." And in sum- 

 marizing the arguments for and against the near alliance of the 

 Dijjnoi with Dipterus and Ctenodus^ after adducing on one 

 side certain points of agreement, he gives on the other the 

 following as points of difference : — 



A. Leindosireyi, Protopterus^ Ceratodus. " Autostylic j no 

 gular plates ; archipterygium ; diphycercal." 



B. Dipterus^ Ctenodus. " Hyostylic ? ; gular plates ; ar- 

 chipterygium ? ; heteroccrcal [Dipterus) ." 



Finally, he is " inclined to hold that on the whole A and B 

 are not ordinarily se])arable, but that they represent two fami- 

 lies or suborders of Ganoids, which may continue to be called 

 Sirenoidei (Dipnoi) and Ctenododipterini." 



That Ceratodus and Dijderus represent two perfectly dis- 

 tinct '■^families " has, however, been already amply shown by 

 Dr. Giinther ; the real question is whetlier or not these two 

 families ought to be classed in the same "order" or "subor- 

 der." Do we, with Joliannes Miiller and Prof. Huxley, 

 consider the Dipnoi and Ganoidei independent " orders " of 

 fishes ? If so, are Dipterus and Ctenodus Dipnoans, or are they 

 Ganoids ? If, on the other hand, we look upon the Dipnoi as 

 being merely a" suborder " of the Ganoidei, does the Cteno- 

 dodipterine family belong to that suborder or to the Crosso- 

 pterygii, or does it likewise constitute an independent " sub- 

 order " by itself? 



Whatever value may be placed upon the position of the 

 nasal apertures, it appeared to me, at the time Dr. Giinther's 

 paper was published, that his reasoning as to the position of 

 Dipterus was irresistible, whether we agree with him in con- 

 sidering the Dipnoi a mere suborder of the Ganoidei or not. 

 In view, therefore, of recently expressed doubts, it becomes of 

 some im])ortance to ascertain whethei' the extraordinary simi- 

 larity between Ceratodus and Dipterus in the form and ar- 

 rangement of the dental plates and palato-pterygoid bones be 

 not (as might be expected to be the case) accompanied by 

 other important correspondences in the general structure of the 

 head, and more especially whether the skull of Dipterus pre- 

 sents that same " autostylic " cliaracter, which Prof. Huxley 

 considers, and I think rightly, to be a feature of ordinal 



