574 TELEOSTEI chap. 



strength, as such an agreement in the structure of so complicated 

 and specialised an apparatus can only be the result of a com- 

 munity of descent of the families which are possessed of it. It 

 is invaria.bly the anterior four vertebrae that take part in the 

 support of the Weberian apparatus. The first vertebra is much 

 reduced ; its upper arch is absent and replaced by the ossicles 

 termed claustricm and scaphiu7n ^ (the former being perhaps 

 nothing but the modified nem'al arch), which fill in the space 

 between the exoccipital and the neural arch of the second 

 vertebra ; the principal piece of the apparatus, the trijius, vari- 

 able in form, is related to the third vertebra, of which it is 

 regarded as a modified rib ; a fibrous ligament extends from the 

 anterior extremity of the tripus to the scapMum,, and in this 

 ligament is inserted the fourth piece, the intercalarium. The 

 various forms of this sub-order also show a complete agreement 

 in the spinal nerves which pass through these ossicles. The 

 parietal bones either separate the frontals from the supra- 

 occipital or are fused with the latter. 



This sub-order is divided into six families. The Characinids 

 are the most generalised, and the others are probably derived 

 from them in the manner expressed by the following diagram: — 



Loricariidae Aspreclmidae 



Cijprinidae Siluridae Gymnotidae 



Characinidae. 



Synopsis of the Families 



I. Parietal bones distinct from tlie supraoccipital ; symplectio present ; 

 ribs mostly sessile, all or tbe greater number of the praecaudal vertebrae 

 without parapopbyses. 



Mouth not protractile, usually toothed ; pharyngeal bones normal ; body 

 scaly ; an adipose dorsal fin often present . 1. Characinidae. 



Mouth not protractile, usually toothed ; pharyngeal bones normal ; body 

 Eel-shaped, naked or scaly ; vent under the head or on the throat 



2. Gymnotidae. 



^ For the nomenclature of these ossicles, cf. Bridge and Haddon, Proc. Soy. Soc. 

 xlvi. 1889, p. 310. 



