41 o NATURAL SCIENCE. June. 



along the trunk; in the Mesozoic Chondrosteidae, of which A. S. 

 Woodward figures a finely preserved specimen from the Lower Lias 

 of L5'me Regis, the upper lobe of the tail is covered with fulcra and 

 scales as in the living Polyodontidae, while the rest of the body is 

 naked. In the Acipenseridae, besides this covering of the caudal lobe, 

 there are several longitudinal series of large bony plates with smaller 

 star-shaped ossifications between. No one will deny that the 

 Chondrosteidae, Polyodontidag, and Acipenseridae stand in the closest 

 genetic connection, though the future of the Belonorhynchidae is still 

 very doubtful; but that these cartilaginous ganoids of J. Miiller, so 

 remarkably different from the typical ganoids, may probably be 

 derived from the Palaeozoic Palaeoniscidae, is one of the most important 

 results of the always exact researches of R. H. Traquair. Neverthe- 

 less, whether it is correct to place these primitive scaly forms in the 

 same order as the cartilaginous ganoids, appears doubtful, since even 

 A. S. Woodward points out that between the Triassic Catopteridae 

 and the older Palaeoniscidae there is as close a connection as between 

 the former and the earliest representatives of the Lepidostei. In any 

 -case, it is no breach of existing rules of classification to arrange the 

 primitive ancestral forms in a special group opposed to one comprising 

 their later descendants, which are specialized in various directions. 



The Lepidostei or Lepidosteoidei, Pycnodonti, and Amioidei, as 

 hitherto understood, are divided by A. S. Woodward into the three 

 sub-orders of Protospondyli, Aetheospondyli, and Isospondyli. The 

 Protospondyli correspond to the Lepidostei of Huxley, with the 

 exception of the Aspidorhynchidae and Lepidosteidse, for which 

 Woodward establishes a special sub-order (Aetheospondyli), which, 

 however, he regards as of only provisional significance, since " the 

 recognition of this group is a confession of ignorance," in consequence 

 of the uncertainty of the origin and relationships of the two families 

 placed here. The name Aetheospondyli is in allusion to the unique 

 variations of the vertebral centra from the bi-concave or amphicoelous 

 to an opisthocoelous type. 



The Protospondyli form an unusually numerous derivative series 

 from the primitive Chondrostei, or Heterocerci, as I have termed them. 

 Their vertebral column is never completely ossified but shows different 

 stages in the process of ossification, in part most remarkably suggestive 

 of those observed among fossil Amphibia. In outward aspect and 

 squamation the Protospondyli are most closely connected with their 

 fore-runners, but the caudal fin loses its conspicuous heterocercy, the 

 upper lobe is atrophied, and the caudal becomes hemi-heterocercal or 

 only internally heterocercal ; the number of supports in the dorsal 

 and anal fins becomes exactly equal to that of the dermal rays ; the 

 clavicle and cleithrum are fused together ; the opercular apparatus, 

 i.e., the preoperculum, is reduced, and the baseosts of the pelvis 

 disappear. Most of the families of Protospondyli are closely connected, 

 so that their definition is difficult ; they were probably already 

 differentiated at the beginning of the Mesozoic period. 



The section on the Protospondyli abounds in new and important 

 observations ; it forms the main part of the third volume. The sub- 

 division of this great order from which the typical Teleostei have 

 arisen, into the families of Semionotidae, Macrosemiidas, Pycnodontidae, 

 Eugnathidae, Amiidae, and Pachycormidae, is much better than all 

 previous attempts at classification. The Semionotidae correspond 

 to the Stylodontes and Sphacrodontes of A. Wagner, and com- 

 prise fishes with thick shining rhombic ganoid scales, which are 

 closely related to the Catopteridae in their anatomical characters and 



