TRANSACTIONS OF SECTION D. 781 



Catopteridffi are obviously an annectent group, as, altliougli from tlieir abbreviate 

 heterocercal tail they have usually been placed in the next sub-order, Dr. Smith 

 Woodward prefers to look upon them as Chondrostei (i.e. Acipenseroidei).' 

 AVherever we place them they express the beginnin<j of a set of changes towards 

 a more modern type of fish, which are emphasised in the great series of Lepidos- 

 teold fishes (Protospondyli + ^Etbeospondyli of Smith Woodward), being the fishes 

 more or less allied to the recent Bony Pilie of North America. 



But these changes must have been well advanced before the Triassic era, for 

 already in the Upper Permian occurs the genus Acentrophorus, whose fellowship 

 with Semionotus, Lepidotus, and all the rest of the series of Mesozoic semi-hetero- 

 cercal ' Ganoids' is at once obvious. 



If we look at the configuration of a typical Jurassic member of this series, such 

 as Lepidotus or Eugnathus, we shall at once see that we are a .stage nearer the 

 modern osseous fish. Though the scales are bony, rhombic, and ganoid, we are 

 struck by the ' Teleostean '-like aspect of the external bones and plates of the 

 head, the rays of the dorsal and anal fins are fewer and correspond in their number 

 to that of the internal supports or ' interspinous ' bones, while in the caudal we 

 see again the semi-heterocercal or abbreviate-heterocercal condition we noticed 

 above in Catopterus. 



Then if we refer to the tail of Lepidosteus itself we shall observe how few are 

 its rays and how evident it is that we have here to do only with the lower lobe of 

 the original palaeoniscoid caudal fin. For a convincing corroboration of this we have 

 only to look at the tail of the embryo Lejndosteus as described and figured by 

 Prof. A. Agassiz to see that it in reality passed through an Acipenseroid stage, 

 and the last we see of the upper lobe of this tail is in the form of a filament 

 ■which projects from the top of the original lower lobe and then disappears. 



Again, in these Lepidosteid forms we have a repetition of the same tendency 

 for the thick rhombic peg-and-socket articulating scales to become rounded and 

 imbricating as we saw in the Crossopterygii and again iu the Palfeoniscidae. So, 

 for instance, in Caturus, which has been shown by Dr. Smith Woodward to 

 resemble Eugnathus so closely in structure, the scales are deeply overlapping, and 

 most of them ' cycloidal ' in shape. To such an extent does this go that in the 

 recent Ainia, whose skeletal structure so clearly shows it to belong to this group, 

 the rounded scales are so thin and flexible that after it was removed from the 

 Clupeoid family, or Herrings, and placed among the 'Ganoids,' it was considered 

 to be the type of a distinct sub-order of 'Amioidei.' Ten years ago, however, 

 Dr. Beard came to the conclusion, from anatomical and embryological data, that 

 this division could no longer be maintained, and that the Amioids must in fact 

 be united with the Lepidosteids.^ Dr. Smith Woodward has, therefore, in the 

 third volume of his catalogue, done well to reduce the 'Amioidei' to the rank 

 of a family, including also the Jurassic genera Liodesmus and Megalurus, and to 

 place this family close to the Eugnathidce. 



As the Acipenseroid s dwindled away after the close of the great Paljeozoic 

 era, and are now scantily represented only by the degenerate paddle-fishes and 

 sturgeons, so the Lepidosteid series, flourishing greatly in the Trias and Jura, in their 

 turn declined in the Cretaceous, and in the Tertiary period became about as much 

 a thing of the past as they are now, the North American Lepidosteus and Amia, 

 of which remains of extinct species have also been found in Eocene and Miocene 

 rocks, only remaining. These two genera can, however, hardly be called ' degenerate.' 



But that the fishes which succeeded the Lepidosteids in populating the seas 



' Dr. Smith Woodward also refers the singular Belonorhynchidas of the Trias to 

 the same sub-order on account of the excess of the number of the dermal rays of the 

 dorsal and anal over that of their supporting ossicles, even although the tail is here 

 abbreviate diphycercal. 



- 'The Inter-relationships of the Ichthyopsida,' Anatomischer Anzeiger, 1890. 

 Smith Woodward arrived at the same result in 1893 from the study of the Jurassic 

 genera Lepidotus and Dapednis. See Proo. Zool. Soc. Land. June 20, 1893, pp. 559- 

 565. 



