96 



LOWER VERTEBRATES. 



the development of the bichir and its allies, we know nothing. The single species of 

 Calamoichthys, C. calabaricus, as its name indicates, comes from Old Calabar, West 

 Africa. 



Oedeb VI. — GINGLYMODI. 



The gar-pikes present an approach to the bony fishes in many respects. They 

 ha^e a bony skeleton, the bones of the fins rudimentary, the spiral valve of the 

 intestine poorly developed. The body is covered with closely placed rhomboid scales, 

 and the shingle-like fulcra are present on the fins. The vertebrae are convex in front 

 and concave behind, forming ball and socket joints, the tail heterocercal, and the 

 ventral fins are between the pectorals and anal. 



The family Lepidotid^ was almost entirely confined to the mesozoic strata, only 



Fig. 70* — Zepidosteus osseus, gar-pike. 



a few, like Pakeoniscus, extending back into the carboniferous. The Lepidosteid.e 

 appeared in the Laramie or fresh-water cretaceous, and to-day only three or four 

 species exist, all confined to our continent. The gar-pikes are all long and slender 

 fishes, covered with hard scales laid on in oblique series, forming a very hard 

 armor. The external bones of the skull are hard and roughened, and the beak is 

 long and flattened, the upper jaw being longer than the lower. The dorsal fin 

 is small, and placed very far back upon the body. In the degree of development of 

 the air bladder and the gills, the gar-pikes are very like the lung-fishes. The 

 bladder is divided up into a number of cellular cavities, recalling at once a rudi- 

 mentary lung, and communicates with the oesoishagus by a slit-like glottis. Besides, 

 it receives the blood-vessels from the aorta. Not only is this organ like a lung 

 in structure, but it functions as such to a certain extent. Two genera of gar- 

 pikes have been indicated, Xepidosteus and Litholejns, but their distinctness is 

 fiuestioned. The most common species is the common gar-pike, or, as it is frequently 



