PA LAEONISCOIDEI 3 > 3 



and trunk, which become very much compressed and deepened, and the 

 accompanying extension of the dorsal and anal fin, the Platysomidae 

 closely resemble the Palaeoniscidae (Fig. 290). Eurynotus, Mesolepis, and 

 Platysomus are three stages in change of form. As the body deepens the 

 scales become transversely elongated, the articular pegs being at their 

 upper end (Fig. 191). The jaws become more pointed, and the pelvic fins 

 become reduced in size (Platysomus), or apparently disappear altogether as 

 in Gheirodus. No symplectic is known, the hyomandibular becomes. nearly 

 vertical, and the mouth is diminished (Fig. 291). The teeth may be 

 considerably modified, becoming swollen and tritoral. In Gheirodus and 

 Gheirodopsis the palatal and splenial teeth fuse to grinding plates. This 

 family is found in Carboniferous and Permian strata [444, 448]. 



,hm>. 

 -sop. 



Fia. 291. 



Oheirodus granulosus, Young. Restoration showing the bones associated with the mandibular 

 and hyoid arches. (Alter Traquair.) ag, angular; ar, articular; d, dentary ; hm, hyomandi- 

 bular ; nipt, metapterygoid ; n, position of nostril ; o, orbit ; op, opercular ; pop, preopercular ; 

 pt, pterygoid ; q, quadrate ; sop, subopercular ; sp, splenial. 



Eurynotus, Ag. ; Mesolcpis, Young (Fig. 290); Wardichthys, Traq. ; 

 Gheirodus, M'Coy ; Cheirodopsis, Traq. ; Carboniferous, Great Britain. 

 Globulodus, Miinster ; Permian, Europe. Platysomus, Ag. ; Carboniferous 

 and Permian, Europe. 



Family Catopteridae. A triassic family of fusiform fish resembling 

 the Palaeoniscidae in general structure ; but with an abbreviate hetero- 

 cercal tail, and lepidotrichia which only slightly exceed the radials in 

 number. The latter also appear to be formed chiefly of one long 

 proximal segment. In the characters just mentioned the Catopteridae 

 undoubtedly approach the Holostei, with which they should possibly be 

 classified. The head and shoulder girdle are quite Palaeoniscid. The 

 ganoid scales are rhombic; the teeth slender and conical [505]. 



Gatopterus, Redf. ; Trias, N. America. Didyopygr, Eg. (Fig. 292) ; 

 Trias, N. America and Europe. 



