106 PISCES. 



widely distributed Cretaceous genus Anomoeodus sometimes 

 seems to exhibit degeneracy in its tritoral dentition. 



The Eugnathidae are the forerunners of the modern Amia, 

 and though the extreme types are widely different, it is very 

 difficult to separate them from the Amiidae in a brief definition. 

 They are fusiform or elongate fishes with wide gape and pointed 

 teeth. The mandibular suspensorium is nearly vertical or 

 inclined backwards, and the snout is not produced, the 

 premaxillae being separate and in contact mesially. The 

 notochord is usually persistent, the vertebrae being very rarely 

 more than incomplete rings. The cranial and facial bones are 

 moderately robust, externally enamelled, and the opercular 

 apparatus is complete. The fin-rays are robust, articulated 

 and divided distally ; fulcra are conspicuous. The dorsal fin 

 is short and acuminate. The scales are rhombic, sometimes 

 with rounded postero-inferior angle. 



FIG. 75. 



Euynathus orthostomus ; restoration, about one-seventh nat. size. L. Jurassic 

 (L. Lias) ; Dorsetshire. (From Brit. Mus. Catal.) 



Eugnathus (tig. 75). An elongate-fusiform fish, covered with rhombic 

 scales. The chondrocranium is well ossified, with a straight basicranial 

 axis, but it has not been sufficiently exposed for precise description. Its 

 base is sheathed by a large parasphenoid, which appears to terminate in 

 advance of the occiput ; and there is a pair of small vomers in front. The 

 membrane-bones of the cranial roof form a continuous shield, which is 

 nearly flat ; the parietals and squamosals are small, the frontals very 

 large, while both postfrontals and prefrontals are invested with superficial 

 membrane-elements. The cheek is completely covered with thin plates, 

 comprising one circumorbital ring, two very large suborbitals (or post- 

 orbitals), and at least one preorbital. The maxilla has a stout, inwardly 

 directed process at its anterior extremity, and exhibits a long narrow 

 supramaxilla above its hinder half ; the premaxilla is extended along the 



