64 



PISCES 



CLASS I 



and anal fins continuous with the caudal, which is diphycercal ; scales very 

 large and thin, without a ganoine layer, almost quadrate in shape, but with 



rounded angles ; marked more or less 

 distinctly with reticulations, as in 

 Ceratodus. Dental plates common 

 in the Carboniferous of Europe 

 and North America ; fine portions 

 of skeleton in the English Coal 

 Measures. 



Sagenodus, Owen (Megapleuron, 

 Gaudry; Ptyonodus, Cope). As 

 Ctenodus, but dental plates with fewer 

 ridges, and median occipital plate 

 with another unpaired plate im- 

 mediately in front of it. Scales and 

 dental plates common in the Carboni- 

 ferous and Lower Permian of Europe 

 FlG ' 11S ' and North America : fine skeletons in 



Palaedaphus insiqnis, van Beneden and de Koninck. . <• -r> i • i 



Imperfect inaudible, i/ 4 nat. size. Devonian ; Liege, the Lower Permian 01 Jbohemia and 



, Tooth; d, Dentary; op, Splenial; y, Lateral fossa. Xj\.„r,„ p 



(after Traquair). x 1 tillLt! - 



Order 2. SIRENOIDEI. 



Cranial roof bones large and few. Rays of median fins very fine, much more 

 numerous than their supports, which are directly apposed to the vertebral arches. 



Family 1. Lepidosirenidae. 



A pair of dental plates on the palatine bones, and an opposing pair on the 

 splenials ; also a pair of small cutting teeth on the vomer. Jugular plates absent. 

 Median fin continuous, and tail diphycercal. Body covered with thin, elastic, cycloid 

 scales without a bony basis. Triassic to Recent. 



Of the three genera referable to this family, Lepidosiren lives in the tropical 

 swamps of South America, Protopterus in those of Africa, and Ceratodus in the 

 rivers of Queensland. 



Ceratodus, Ag. (Fig. 119), is covered with large, thin cycloid scales; the 

 dorsal and anal fins are continuous with the diphycercal caudal. The pectoral 

 and pelvic fins are fringed with membrane stiffened by fine rays. The upper 

 vertebral arches, spinous processes, ribs, and fin supports are encased in thin 

 bony sheaths. The flattened roof of the skull consists of two large median 

 plates, one behind the other, and two pairs of lateral plates. On the lower 

 side of the chondrocranium there occurs the long parasphenoid {PSph), with 

 its rhombic anterior expansion flanked on either side by the pterygo-palatines 

 (Pt). The latter bones meet in a median suture in front, and each bears a 

 large triangular dental plate (d), with radiating ridges. . The vomerine carti- 

 lage (Vo) bears a pair of sharp, chisel-shaped teeth (d r ). On the splenial of 

 each ramus of the mandible there is also a dental plate with deep, radiating 

 ridges. The opercula, sub-opercula, hyoid bones, and branchial arches are 

 ossified ; the quadrate remains cartilaginous. 



In the living Ceratodus (Epiceratodus, Teller), the upper and lower dental 



