The Ganoids i 5 



with very long dorsal and anal fins. In other respects they are 

 very similar to the Pal&oniscidce, the osteology being the same. 

 The PalcBonlscidcE were rapacious fishes with sharp teeth, the 

 Platysomidoz less active, and, from the blunter teeth, probably 

 feeding on small animals, as crabs and snails. 



The rhombic enameled scales are highly specialized and 

 held together as a coat of mail by peg-and-socket joints. The 

 most extreme form is Platysomus, with the body very deep. 

 Platysomus gibbosus and other species occur in the Permian 

 rocks- of Germany. Cheirodus is similar to Platysomus, but 

 without ventral fins. Eurynotus, the most primitive genus, is 

 remarkable for its large pectoral fins. Eurynotus crenatus occurs 



FIG. 3. Eurynotus crenatus Agassiz, restored. Carboniferous. Family 

 Platysomidce. (After Traquair.) 



in the Subcarboniferous of Scotland. Other genera are Meso- 

 lepis, Globulodus, Wardichthys, and Cheirodopsis. 



Some of the Platysomidce have the interneural spines pro- 

 jecting through the skin before the dorsal fin. This condition 

 is found also in certain bony fishes allied to the Carangidaz. 



The Dorypteridae. Dorypterus hoffmani, the type of the sin- 

 gular Palaeozoic family of Dorypteridae, with thoracic or sub- 

 jugular many-rayed ventrals, is Stromateus-like to all appear- 

 ance, with distinct resemblances to certain Scombroid forms, 

 but with a heterocercal tail like a ganoid, imperfectly ossified 

 back-bone, and other very archaic characters. The body is 

 apparently scaleless, unlike the true Platysomidce, in which the 



