216 Miss 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- 
thodida, which are considered by Professor Huxley to link the 
Ganoids to the Elasmobrauchs, ränge 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 Chondrosteidee, to which group 
the sturgeons belong, were certainly represented in the Jurassic seas, 
and possibly by the gigantic Macropetalichthys in the Devonian. 
Amia calva, the dog fish of the American lakes, is the sole member 
of the sub-order Amiadce The Lepidosteid 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 Crossopterygidce, 
that important group of fringe-finned ganoids, through which Prof. 
Huxley 2 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 always replace the branchiostegal rays, and the scales 
are either rhomboidal or cycloidal. The families Saurodipterini, 
Glyptodipterini, and Phaneropleurini are restricted to the Palseozoic 
rocks. 3 The Ccelacantliini ränge from the Carboniferous to the 
1 Two species, namely, Amia scutata and A. dictyocephala Cope, are referred by 
Prof. E. D. Cope (in tlie Bull, of the United States Geol. and Geog. Survey, No. 1. 
2nd series, 1875) to the genus Amia. They are recorded as occurring in the Tertiary 
Shales of South Park ; apparently a freshwater deposit of later Tertiary age. 
2 Decade x. of the Memoirs of the Geological Survey, 1861 (Classification of 
Devonian Fish). 
3 In the memoir on Tristichopterus alatus, Eg. (Trans. Roy. Soc. Edinburgh, vol. 
27, 1875), Dr. Traquair follows Dr. Günther in associating the Ctenodipterini of 
Huxley ( Cteuodus , Dipterus) with the Dipnoi, hut retains the Phaneropleuridce as 
a sixth family of Crossopterygian ganoids, sub-dividing the remaining families thus : 
1. Polypteridae ; 2. Ccelacanthodae ; 3. Rhombodipteridse, sub-fam. Glyptolcemini 
( Glyptiiltemus , etc.), Saurodipterini ( Osteolepis , Diplopterus ) ; 4. Cyclodipteridse 
{Tristichopterus, etc.) ; 5. Holoptychidse ( Holoptychius , etc.) ; 6. Plianeropleuridae 
{ Phaneropleuron , Uronemus). In the memoir on British Carboniferous Ganoids 
by the same author, published in the vol. of the Pal. Soc. for 1877, the 
Palaeoniscid® are raised to the rank of a distinct family, and removed from the 
sub-order Lepidosteoim: 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. Spatularidaj. 
„ 3. Chondrosteidse, 
Fam. 4. Palaeoniscid®. 
„ 5. Platysomidae. 
Sub-order III. Lepidosteoidsc. 
„ IV. Amioidei. 
