604 



The Crossopterygii 



Lepisosteus. In Glyptopomus these scales are sculptured, in 

 the others smooth. In Osteolepis, Thursius, Diplopterus, and 

 Glyptopomus a pineal foramen is present on the top of the head. 

 This is wanting in Parabatrachus (Megalichthys of authors). 

 In Osteolepis, Thursius, and Parabatrachus the tail is heterocercal, 



FIG. 374. Oyroptychius microlepidotus Agassi/,. Devonian. Family Megalich- 



thyidtK. (After Pander.) 



while in Diplopterus and Glyptopomus it is diphycercal. Osteo- 

 lepis macrolepidotus and numerous other species occur in the 

 Lower Devonian. Diplopterus agassizii is common in the same 

 horizon. Megalichthys hibberti is found in the coal-measures, 

 and Glyptopomus minimus in the Upper Devonian. Palceosteus 

 is another genus recently described. 



The Onychodontida are known from a few fragments of 

 Onychodus sigmoides from the Lower Devonian of Ohio and 

 Onychodus anglicus from England. 



Order Actinistia. In the Actinistia there is a single fin-ray 

 to each basal bone, the axonosts of each ray fused in a single 



FIG. 375. Cadacanlhus elegans Newberry. From the Ohio Carboniferous, showing 

 air-bladder. (After Dean.) 



piece. The notochord is persistent, causing the back-bone 

 in fossils to appear hollow, the cartilaginous material leaving 

 no trace in the rocks. The genera and species are numerous, 

 ranging from the Subcarboniferous to the Upper Cretaceous, 

 many of them belonging to Ccelacanthus, the chief genus of the 



