APPENDIX B 



659 



lary and premaxillary bones in the upper jaw, and with elongate leaflike paired 

 fins having a central skeletal axis; the *lobe-finned fishes (Crossopterygii, Figs. 

 27.15 and 17), with marginal teeth on the maxillary and premaxillary bones and 

 fins with a fleshy base that contains the skeletal elements of the pentadactyl 

 limb, extinct but ancestral to Amphibia; and the coelacanths (Coelacanthi). 1 



Subclass 2. The ray-finned fishes (Actinopterygii) have no internal nostrils; 

 fins with a very short base and consisting chiefly of a membranous web supported 

 by slender horny rays. The principal group of the ray fins is the order Teleosti, 

 the modern fishes (Fig. B.30), which comprises more than 90 per cent of all living 

 species of fishes. In this order the scales are thin and horny or absent altogether, 



Fig. B.29. The northern longnose gar, Lepisosteus osseus oxyurus, a primitive "ganoid "ray- 

 finned fish. (Courtesy Institute of Fisheries Research, Michigan Department of Conservation.) 



and the swim bladder is no longer used as a lung but is purely a hydrostatic 

 organ. 



The first four classes of vertebrates, above, are sometimes all grouped into the 

 single category of Fishes (Pisces). 



Class 5. The Amphibians (Amphibia). "Stegocephalians," salamanders, frogs, 

 toads, and blindworms. Cold-blooded vertebrates partially adapted to land life, 

 with two pairs of pentadactyl limbs except when these have been lost through 

 degeneration. Skull with double occipital condyle. Skin smooth or rough and rich 

 in glands that keep it moist, modern amphibians almost always without skin 

 plates or scales, extinct types with dermal bony plates buried in the skin. Respira- 

 tion usually by gills in the young, by lungs and skin in the adult. Heart three- 

 chambered in adult. Eggs, with few exceptions, laid in water and larval stages 

 aquatic; most adults partly or completely terrestrial but some aquatic throughout 

 life. 



Subclass 1. The Apsidospondyli have "arch vertebrae" in which the centra 

 are formed by fusion of an anterior and a posterior cartilage block. Includes the 



1 The coelacanths, an offshoot of the lobe fins, were supposed to have been extinct 

 since the Cretaceous. But in 1938, a South African fisherman seined up a 5-foot long, 

 blue-scaled marine fish from a depth of 40 fathoms, which proved to be a surviving 

 coelacanth. It was named Latimeria. 



