520 Notices of Memoirs — Dr. R. E. Traquair's Address. 



there can be no doubt that in spite of this their caudal fins are 

 perfectly homologous structures. 



But of special interest is the question of the primitive or non- 

 primitive nature of the continuity of the median fins in the recent 

 Dipnoi. Like others I was inclined to believe it primitive, and that 

 the broken-up condition of these fins in Dipterus was a subsequent 

 specialization, and in fact gave the series Fhaneropleuron, Scau- 

 menacia, Dipterus macropterus, and D. Valenciennesii as illustrating 

 this process of differentiation. This view, of course, draws on the 

 imperfection of the geological record in assuming the existence of 

 ancient pre-Dipterian Dipnoi with continuous median fins, which 

 have never yet been discovered. But Dollo, using the very same 

 series of forms, showed good reason for reading it in exactly the 

 opposite direction. 



The series is as follows : — 



1. Dipterus Valenciennesii, Sedgw. & Murch., from the Orcadian 

 Old Eed, and the oldest Dipnoan with whose shape we are acquainted, 

 has two dorsal fins with short bases, a heterocercal caudal, and one 

 short-based anal. 



2. Dipterus macropterus, Traq., from a somewhat higher horizon in 

 the Orcadian series, has the base of the second dorsal much extended, 

 the other fins remaining as before. 



3. In Scaumenacia curta (Whiteaves), from the Upper Devonian 

 of Canada, the first dorsal has advanced considerably towards the 

 head, and its base has now become elongated, while the second has 

 become still larger and more extended, though still distinct from the 

 caudal posteriorly. 



4. In Phaneropleuron Andersoni, Huxley, from the Upper Old Eed 

 of Fifeshire, the two dorsal fins are now fused with each other and 

 with the caudal, forming a long continuous fin along the dorsal 

 margin, while the tail has become nearly diphycercal, with elonga- 

 tion of the base of the lower division of the fin. But the anal still 

 remains separate, narrow, and short-based. 



5. In the Carboniferous JJronemus lobatus, Ag., the anal is now 

 also absorbed in the lower division of the caudal, forming likewise 

 on the hasmal aspect a continuous median fin behind the ventrals. 

 There is also a last and feeble remnant of a tendency to an upward 

 direction of the extremity of the vertebral axis. 



6. In the recent Ceratodus Forsteri, Krefft, the tail is diphycercal 

 (secondary diphycercy), the median fins are continuous, the pectorals 

 and ventrals retain the biserial archipterygium, but the cranial roof- 

 bones have become few. 



7. In Protopterus annectens, Owen, the body is more eel-like, and 

 the paired fins have lost the lanceolate leaf-like appearance which 

 they show in Ceratodus and the older Dipnoi. They are like slender 

 filaments in shape, with a fringe on one side of minute dermal rays ; 

 internally they retain the central jointed axis of the ' archipterygium,' 

 but according to Wiedersheim the radials are gone, except it may be 

 one pair at the very base of the filament. 



8. Finally, in Lepidosiren paradoxa, Fitz., the paired fins are still 



