The Crossopterygii 603 



The Holoptychiidce have the pectoral fins acute, the scales 

 cycloid, enameled, and the teeth very complex. Holoptychius 

 nobilissimus is a very large fish from the Devonian. Glyptolepis 

 leptopterus from the Lower Devonian is also a notable species. 

 Dendrodus from the Devonian is known from detached teeth. 



In the Ordovician rocks of Canon City, Colorado, Dr. Wal- 

 cott finds numerous bony scales with folded surfaces and stellate 

 ornamentation, and which he refers with some doubt to a 

 Crossopterygian fish of the family Holoptychiidce. This fish he 



FIG. 373. Basal bone of dorsal fin, Holoptychius leptopterus (Agassiz). 

 (After Woodward.) 



names Eriptychius americanus. If this identification proves cor- 

 rect, it will carry back the appearance of Crossopterygian fishes, 

 the earliest of the Teleostome forms, to the beginning of the 

 Silurian, these Canon City shales being the oldest rocks in which 

 remains of fishes are known to occur. In the same rocks are 

 found plates of Ostracophores and other fragments still 

 more doubtful. It is certain that our records in palaeontology 

 fall far short of disclosing the earliest sharks, as well as 

 the earliest remains of Ostracophores, Arthrodires, or even 

 Ganoids. 



Megalichthyidae. The Megalichthyidce (wrongly called " Rhizo- 

 dontidaz ") have the pectoral fins obtuse, the teeth relatively 

 simple, and the scales cycloid, enameled. There are numer- 

 ous species in the Carboniferous rocks, largely known from 

 fragments or from teeth. Megalichthys, Strepsodus, Rhizo- 

 dopsis, Gyroptychius , Tristichopterus, Eusthenopteron, Cricodits, 

 and Sauripterus are the genera; Rhizodopsis sauroides from 

 the coal-measures of England being the best-known species. 



The Osieolepidaz differ from the Megalichthyida mainly in 

 the presence of enameled rhomboid scales, as in Polypterns and 



