GANOIDEI. 363 



and grows to a length of about six feet, of which the rostral 

 shovel takes about one-fourth ; in young examples it is com- 

 paratively still longer. 



PsEPHDEUS differs from Polyodon in having the rostral 

 process less depressed and more conical. The gill-rakers are 

 comparatively short, in moderate number, and distant from one 

 another. Upper caudal fulcra enormously developed, and in 

 small number (six). 



PsephuTus gladius inhabits the Yan-tse-Kiang and Hoangho, 

 the distribution of the Polyodontidm beiug perfectly analogous 

 to that of ScaphirJiynchus. It grows to an immense size, 



Fig. 143. — Psephurus gladius. 



specimens of 20 feet in length being mentioned by Basilewsky. 

 The function of the rostral process in the economy of these 

 fishes is not yet sufficiently explained. Martens believes that 

 it serves as an organ of feeling, the water of those large Asiatic 

 and American rivers being too turbid to admit of the Sturgeon 

 seeing its prey, which consists of other fishes. The eyes of 

 Psephurus, as well as Polyodon, are remarkably small. Both 

 fishes are used as food. 



Allied to the Polyodontidce, and likewise provided with a 

 paddle-shaped production of the fore part of the head, is the 

 fossil genus Chondrosteus, remains of which occur in the Lias. 



FIFTH SUB-OEDEE— POLYPTEEOIDEI. 



Paired fins ivifh axial skeleton, fringed ; dorsal fins two or 

 vnore. Branchiosfegals absent, hut generally gular plates. Ver- 

 tebral column diphycercal or heterocercal. Body scaly. 



