MUG1LI FORMES 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. 



Pentanemus, 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 rhomboidul 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 ; Stromctieutt, 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. ; Acrotiis, 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. 423. 

 Ophioccphalus utriutus, 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. 



