﻿216 Hiss Agnes Crane — On Certain Living and Fossil Fishes. 



and rivers of North America. The preservation of the majority of 

 living ganoids in America is probably owing to the fact that some 

 portions of this ancient continent, truly the old world of geologists, 

 have never been submerged since their upheaval from the first 

 Silurian seas ; thus some representatives of this ancient race of fishes 

 were able to find a refuge in its bays and rivers, and the chain 

 of descent has been kept unbroken from the early ages of the 

 incalculably remote past. The large-spined, shagreen-sealed Acan- 

 thodidcg, which are considered by Professor Huxley to link the 

 Ganoids to the Elasmobranchs, range only in the Devonian and 

 Carboniferous rocks. The "thick-toothed" Pycnodonts lived from 

 the Coal-measures to the Tertiaries, and are now extinct, while the 

 buckler-headed Cephalaspids, like the Placoderms, existed only in 

 Silurian and Devonian times. The CJiondrosteidce-, to which group 

 the sturgeons belong, were certainly represented in the Jurassic seas, 

 and possibly by the gigantic IlacropetaUchthys in the Devonian. 

 Amia calva, the dog fish of the American lakes, is the sole member 

 of the sub-order Amiadm} The Lepidosteidce includes the living 

 bony pikes, inhabitants of the rivers of the same continent, and fossil 

 forms in all the formations reaching back to the Devonian. 



There remains for discussion but the sub-order Crossopterygides, 

 that important group of fringe-finned ganoids, through which Prof. 

 Huxley '^ considers the passage from the fishes to the reptiles took 

 place. All the families of this well-defined sub-order are character- 

 ized by the possession of lobate paired fins having a central axis or 

 stem covered with scales like the body walls, and surrounded by a 

 fringe of fin rays. Two dorsal fins are present in the majority. 

 Jugular plates alwaj's replace the branchiostegal rays, and the scales 

 are either rhomboidal or cycloidal. The families Saurodiptertni, 

 Glyptodipterini, and Phaneropleurini are restricted to the Palceozoic 

 rocks.* The CoelacantMni range from the Carboniferous to the 



^ Two species, namely, Amia scutata and A. dictyocephala Cope, are referred by 

 Prof. E. D. Cope (in the Bull, of the United States Geol. and Geog. Survey, No. 1. 

 '2nd series, 187o) to the genus Amia. They are recorded as occurring in the Tertiary 

 Shales of South Park ; apparently a freshwater deposit of lat«r Tertiary atre. 



* Decade x. of the Memoirs of the Geological Survey, 1861 (Classification of 

 Devonian Fish). 



s In the memoir on TristicJiopterus alatus, Eg. (Trans. Roy. Soc. Edinburgh, vol. 

 27, 1875), Dr. Traquair follows Dr. Giinther in associating the Gtenodipterini of 

 Huxley [Olei'Odus, I)ipterus) with the Dipnoi, but retains the Phaneropletiridce as 

 a sixth family of Crossopterygian ganoids, sub-dividing the remaining families thus : 

 1 . PolypteridiB ; 2. Coelacanthodae ; 3. Ehombodipteridse, sub-fani. Glyptolcemini 

 {G-lypUilcemm, etc.), Saurodipterini [Osteolepis, Diplopterns) ; 4. C3'clodipteridae 

 {Tristichopterus, etc.); 5. Holoptychidse {Holopti/chius, etc.); 6. PhaneropleuridiB 

 {Phaneropkuron, Uronemits). In the memoir on British Carboniferous Ganoids 

 by the same author, published in the vol. of the Pal. Soc. for 1877, the 

 Palseoniscidse are raised to the rank of a distinct family, and removed from the 

 sub-order Lepidosteoidje into that of the Acipenseroidei. The Dipnoi are 

 retained as a separate order, and the following classification is proposed for the 

 order Ganoidei. 

 Sub-order I. Crossopterygii. 

 II. Acipenseroidei. 



Fam. 1. Acipenseridse. 

 ,, 2. Spatularida3. 

 „ 3. Chondrosteidse. 



Fam. 4. Palaeoniscidae. 

 ,, 5. Platysomidse. 

 Sub-order III. Lepidosteoidse. 

 „ IV. Amioidei. 



