MUG1LIFORMES 421 



scapula to form a ventral prolongation, supporting a fascicle of fila- 

 mentous dermal rays separate from the main fin (Fig. 422) ; a highly 

 specialised condition. 



Pentanermis, Art. ; Polyncmus, L. ; Galeoides, Gthr. tropical seas. 



TRIBE 2. 



With one dorsal fin, of which the front portion may be spinous. 

 The anterior vertebrae without parapophyses and with sessile ribs. 



SUB-TRIBE A. The dentition is very feeble ; the pseudobranch is 

 provided with a row of gill-rakers ; and the oesophagus has two lateral 

 pouches beset with internal papillae. 



Family TETRAGONURIDAE. With a pair of lateral keels near the end 

 of the tail ; specialised rhomboidal scales set in obliquely transverse 

 rows, in each of which the scales are connected together ; and with free 

 pelvic girdle. The air-bladder is lost. 



Tetragonurus, Risso ; warm seas. 



Family STROMATEIDAE. These are closely related to the preceding ; 

 but they have cycloid scales, the pelvic bones may be attached by liga- 

 ment to the cleithra ; and the body becomes very deep and compressed, 

 much as in Lampris. The air-bladder and the pelvic fins may be lost. 



Nomeus has enormous pelvic fins, which fold in ventral grooves. 



Platycormus, V. D. M. ; Homosoma, Eocene. Nomeus, Cuv. ; Cubiceps, 

 Lowe ; Stromateus, Art. ; Centrolophus, Lac. 



SUB-TRIBE B. Family ICOSTEIDAE. Although lacking both spines 

 and oesophageal pouches, the aberrant Rag-Fish are probably allied to 

 the Tetragonuridae, which they resemble in the possession of gill-rakers 

 near the pseudobranch. The vertebrae have increased in number (70) ; 

 the scales when present are cycloid, and the pelvic bones are free. 



Icosteus, Lock ; Icichthys, J. and G. ; Acrotus, Bean Pacific American 

 coast. 



TRIBE 3. 



The head is covered with large scales ; there are generally para- 

 pophyses bearing the ribs ; and a distinguishing character is the 



FIG. 4:23. 

 Ophiocephalus striatus, India. (After Giinther.) 



possession of an accessory suprabranchial chamber. The branchiostegal 

 membranes are confluent below the isthmus. The pelvic bones are joined 

 by ligament to the cleithra. 



