2 Dr. R. H. Traquair on the Genus Diptems. 



shown by Pander *, who gave an excellent account of the 

 structure of Dipterus, and proposed to institute for it the new 

 family of Ctenodipterini, a term afterwards altered by Sir 

 Philip Grey-Egerton into Ctenododipterini f. This family, 

 in which Geratodus % and Cheirodits were also provisionally 

 included, was accepted by Prof. Huxley, and placed by him 

 in his suborder Crossopterygidse §. Moreover, in a remark- 

 able and oft-quoted passage, he drew attention to the singular 

 relations subsisting between the living Protopterus and the 

 cycliferous Crossopterygidte, especially as regards those of the 

 latter which have acutely lobate paired fins. Though Prof. 

 Huxley did not class the Dipnoi as Ganoids, nor Dipterus as 

 a Dipnoan, he struck the keynote to its real position in the 

 sentence : — " Furthermore Lepidosiren is the only fish whose 

 teeth are comparable in form and arrangement to those of 

 Dipterus.^'' 



The discovery of Geratodus Forsteri in the rivers of Queens- 

 land, and its addition to the catalogue of living Dipnoi, threw 

 a fresh flood of light on the subject; and Dr. Giinther was not 

 long in following up the idea suggested in Prof. Huxley's 

 remark quoted above. Guided chiefly by the obvious simi- 

 larity in Dipterus and Geratodus of the bones of the lower 

 aspect of the skull and of the mandible, the dentition, the want 

 of distinct maxillary and pra^maxillary elements, the position of 

 the nasal apertures, the notochordal vertebral axis, the acutely 

 lobate condition of the paired fins, and the cycloidal scales, 

 Giinther proposed to actually include the Ctenododipterini as 

 a family of Dipnoi, looking upon these Dipnoi, however, not 

 as a distinct order of fishes, but merely as a "suborder" of the 

 Ganoidei. On the other hand the leading differences between 

 Dipterus and Geratodus^ as indicated by Giinther, may be 

 summarized as follows : — the heterocercy of the former genus, 

 its dorsal fin being divided into two, the enamelled surface of 

 its scales, the enamelled scutes of its cranial buckler, its gular 

 plates, the dermal rays of the median fins being joined to the 

 extremities of the interneural and interhsemal spines, the latter 

 being branched at their distal ends, and, finally, some unes- 

 sential differences in the microscopic structure of the dental 

 plates. Yet, " weighing the points of affinity and difference 

 against each other," Dr. Giinther observes, " we must come 



* 'Ueber die Ctenodipterinen des devomschen Systems/ St. Peters- 

 burg, 1858. 



t Dec. Geol. Sui-vey, x. 1861, p. 55. 



X Beyi-ich had, indeed, previoiLsly noticed the resemblance between 

 the dental plates of Dipteinis and Geratodus ('Zeitschrift der deutschen 

 geolog. GeseUsch.' 1850, p. 154). 



§ Dec. Geol. Survey, x. 1861. 



