SILUROIDS. 87 



projects from the premandibular and vomerine bones, and one or 

 more rows of similar teeth from the intermaxillaries. The corre- 

 sponding teeth in the Doras are either minutely villiform, or are 

 replaced by equally minute uncalcified papillce, which permanently 

 represent the very earliest stage of dental development. 



The slightly calcified papillae on the intermaxillary and pre- 

 mandibular bones of the Hypophthalmus are so minute as to require 

 the aid of a pocket lens for their detection : but the branchial arches 

 support more conspicuous organs, which are clearly referable to 

 the dental system :(1) these are slender, elongated, pointed, whitish, 

 rigid, and fragile lamellae, attached in a close-set row to the concave 

 side of the arch, and wdth their points projecting towards the gullet. 

 Those of the first pair of branchial arches are most developed, 

 equalling the gills in length ; the rest gradually diminish as they ap- 

 proach the pharynx. 



In the Pimelodus villiform teeth are arranged in several rows upon 

 the intermaxillaries and premandibulars, and a few graniform teeth 

 upon the vomer (Pimel. Spixii). In the Pimelodus ctenodus, the first row 

 of jaw-teeth is composed of larger, rounded conical denticles, with an 

 obtuse apex. Other species of Pimelodus have teeth on the palatine 

 bones, but not on the vomer : and the species called by Cuvier Pi- 

 melodus genidens offers the singular peculiarity of a patch of moveable 

 calcified denticles upon the inside of each cheek, or lateral membrane 

 closing the mouth. 



In the genus Platy stoma, the intermaxillary, premandibular and 

 vomerine bones are beset with broad bands of strong villiform and 

 setiform teeth gradually increasing in length as they are placed deeper 

 in the mouth :(2) the pharyngeal arches are covered with similar, but 

 finer denticles. 



In the Plotosi, the vomerine teeth are obtuse and rounded. 



The premandibular teeth of the Synodontes present compressed 

 crowns terminated at one end by a recurved apex, and attached by 

 the opposite end or base to a flexible peduncle. (3) 



(1) Agassiz, Spix, Pisces Brazilienses, p. 15. 



(2) PI. 1, fig. 1, exhibits the under surface of the right intermaxillary bone of a Siluroid 

 fish of the subgenus Platystoma. 



(3) " La machoire inferieure porte un paquet de dents tres applaties lateralement, terminees 



