176 SUB-CLASS GANOIDEI. 



Sub-order 2. CLADISTIA. 



Notochord more or less constricted and replaced by ossified vertebrae. 

 Baseosts in median fins rudimentary or absent ; axonosts of dorsal fins 

 equal in number to the apposed dermotriohia. Pectoral fins di- or tri- 

 basal. Nares on the vipper surface of the snout. 



Fam. 7. Polypteridae. Body covered with rhombic ganoid scales ; 

 vertebral cokunn ossified ; tail diphycercal ; pectoral fins tribasal ; two 

 jugvilar plates only ; dorsal fins numerous ; pvilp cavity of teeth simple. 

 Polypterus Geoffr. (Fig. 104), with pelvic fins, rivers of North and 

 Equatorial West Africa ; CalamoicUhys Smith, elongated and without 

 pelvic fins, rivers of Old Calabar and the Cameroons. 



Yir,. 104. — Polypternx hichir (from Claus). 



Order 3. Lepidostei. 



Body covered with rhombic or rhomboidal scales arranged in 

 oblique rows and articulated together. Caudal fin hemi-hetero- 

 cercal. Vertebral column in the most different degrees of 

 ossification. Unpaired, and sometimes paired fins with fulcra. 

 Branchiostegal rays numerous, and often a median jugular plate 

 Always four opercular bones ; between preoperculum and orbit 

 at least one row of postorbitals. Infraclavicle absent. Somactids 

 of the unpaired fins as numerous as the dermotriohia. Teeth 

 pointed or conical. The pelvic fins are ivithout baseosts. 



This order, which appears to be closely allied to the Palaeonis- 

 cidae on the one hand and to the Amioidei on the other, in- 

 cludes the living genus Lepidosteus. With the exception of 

 the Permian genus Acentrophorus, the extinct members are 

 found in the Lias, Jurassic, Lower Cretaceous, and Tertiaries. 



The following remarks apply to the living Lejndosteidae, 

 The body is covered by rhombic scales articulated together 

 (see p. 177). The tail is hemi-heterocercal. The paired fins 

 are non-lobate, and all the fins bear paired fulcra. The jaws 

 are much elongated, forming a snout ; the premaxillae form most 

 of the upper jaw. Both jaws bear teeth, small and large, and 

 there are fine close-set teeth on the palatines and vomers. The 

 vertebrae are well developed and ossified, and have opisthocoelous 

 centra. The chondrocranium is large and cartilaginous with 



