574 TELEOSTEI Crean 
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 invariably 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 claustrum and scaphium' (the former being perhaps 
nothing but the modified neural arch), which fill in the space 
between the exoccipital and the neural arch of the second 
vertebra; the principal piece of the apparatus, the ¢ripus, 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 scaphiwm, 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 :— 
Loricarvidae Aspredinidae 
Cyprinidae Siluridae Gymnotidae 
| 
Characinidae. 
SYNOPSIS OF THE FAMILIES 
I. Parietal bones distinct from the supraoccipital ; symplectic present ; 
ribs mostly sessile, all or the greater number of the praecaudal vertebrae 
without parapophyses. 
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. 
1 For the nomenclature of these ossicles, cf. Bridge and Haddon, Proc. Roy. Soc. 
xlvi. 1889, p. 310. 
