230 The Crossopterygil 
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, 
Fia. 163 —G@Gyroptychius microlepidotus Agassiz. Devonian. Family Megalich- 
tiyide. (After Pander.) 
while in Diplopterus and Glyptopomus it is diphycercal. Osteo- 
lepis macrolepidotus and numerous other species occur in the 
Lower Devonian. Diplopterus agassizit is common in the same 
horizon. Megalichthys hibberti is found in the coal-measures, 
and Glyptopomus minimus in the Upper Devonian. Pal@osteus 
is another genus recently described. 
The Onychodontide 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 
Fia. 164 —Calacanthus 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 Calacanthus, the chief genus of the 
