THE ORDERS OF TELEOSTOMOUS FISHES 463 



The earliest known Actinopteran, Cheirolepis , of the Lower Old 

 Red Sandstone and Upper Devonian, forerunner of the Palasoni- 

 scidse, can be readily distinguished from the contemporary and 

 numerous Crossopterygians by its non-lobate paired fins, the 

 archaic form of its heterocercal tail, its lack of paired central 

 gular plates, and the corresponding development of lateral 

 branchiostegal rays, and by its minute rhomboidal, obliquely 

 arranged scales (almost suggesting those of Acanthodian Elasmo- 

 branchs) . This generalized type may be traced on the one hand 

 into the deep-bodied Platysomidse of the Carboniferous and 

 Permian, and, on the other hand, through the Chondrosteidse, 

 into the long-bodied and more or less scaleless and degenerate 

 Sturgeons (Chondrostei) . Possibly on account of the restriction 

 imposed by the simple rhombic type of squamation upon lateral 

 flexures of the body in swimming, we observe: (i) the occurrence 

 of deeply overlapping and even cycloid scales (Coccolepis of the 

 Palseoniscidse) , and (2) the partial or complete suppression of the 

 scales in Phanerosteon of the Palaeoniscidse, Dorypterus of the 

 Platysomidas, and in the entire suborder Chondrostei. It is 

 noteworthy that the early Heterocerci, commonly grouped 

 together in the family Palaeoniscidae, include forms (e. g. Cheiro- 

 lepis, Holurus, Coccolepis) which are so different in several 

 important respects that they might almost be regarded as the 

 types of distinct families. 



The CatopterLdas present a morphological advance in the 

 direction of the Holostei, since they combine a Palasoniscid type 

 of head with an externally homocercal tail. 



Dorypterus of the Upper Permian of Germany, regarded by 

 Smith Woodward as a specialized offshoot from the Platysomidae, 

 is deep-bodied and Stromatceus-like, and suggests Lampris in its 

 general body form and its many-rayed ventrals (Jordan, '05). 



The Belonorhynchidse may be either very aberrant Chon- 

 drostei or "abnormally modified Crossopterygians." 1 There 

 is no trace of heterocercy in the tail (cf. the tail of Eusthe- 



1 Reis, O. M., " Zur Osteologie und Systematik der Belonorhynchiden 

 und Tetragonolepiden," Geogr. Jahresh., 1891 (1892), p. 157 



A. S. Woodward, Cat. Foss. Fishes, Brit. Mus., Part III, 1895, pp. vii, 

 Pl/23. 



