PERCESOCES 



641 



scales. Kibs attached to the extremity of strong parapophyses. 

 Pectoral fin inserted low down, with a lower portion consisting of 

 free rays ; the upper portion, or fin proper, attached to the 

 scapula, the lower to a fenestrate bone which appears to be 

 formed by coalesced pterygials (Fig. 391, pt.\ Ventral fin more 

 or less approximated to the pectoral, with one spine and five soft 

 rays ; pelvic bones suspended from the post-clavicles. Two well- 

 separated dorsal fins, the anterior formed of a small number of 

 spines. Air-bladder, if present, very large. 

 The vertebrae number 24 (10 + 14). 



FIG. 392. Polynemus quadrifilis, x \, (After Cuvier and Valenciennes.) 



Three closely allied genera : Polynemus, Pentanemus, and 

 Galeoides, with about 2 5 species, from the shores of tropical seas, 

 often entering rivers. Some attain a length of 4 feet, and are 

 valued as food or for the isinglass yielded by their air-bladder. 

 The free pectoral filaments are organs of touch, and can be moved 

 independently of the fins. 



Fam. 6. Chiasmodontidae. The deep-sea genera, Chias- 

 modon, Pseudoscopelus, and Champsodon, which have been placed 

 either with the Gadidae, the Trachinidae, or the Berycidae, may 

 be referred to the Percesoces, as the pelvic fins have only a 

 ligamentous connexion with the pectoral arch. Unfortunately, 

 the skeleton has only been examined in Champsodon ; it is 

 remarkably similar to that of the Atherinidae. As in Atherin- 

 ichthys, the posterior extremity of the air-bladder is protected by 

 a bony sheath formed by the expanded ring-like haemal processes 

 of the anterior caudal vertebrae. Vertebrae 32 (16 + 16). The 



VOL. vn 2 T 



