402 H. B. POLLARD, 



outwards. They are also present in Cyprinidae. The coronoid ten- 

 tacle is most typically shown in Trichomycterus, where it is very long. 

 Its base passes continuously into a large procartilaginous root piece, 

 the coronoid piece, which is firmly attached to the cartilaginous 

 coronoid process of the lower jaw. 



In Callichthys the tentacle is fused, near its base, with the mental 

 tentacle, and the coronoid piece is only represented by a small mass 

 of procartilage. The rudimentary tentacles of Hypostomidae are 

 maxillary tentacles. 



The tentacle at the angle of the mouth in the majority of Silu- 

 roids combines the characters of the two tentacles and may thus be 

 termed maxillo-coronoid. In Auchenaspis this, is well shown (Figs. 1 

 and 2). The coronoid piece is seen to be continuous with the tentacle 

 but on the other hand this tentacle is borne by the maxilla, which 

 articulates with the prepalatine piece. In Silurus (Figs. 3 and 4) 

 the coronoid piece does not reach the tentacle actually , but ap- 

 proaches near it. What I think may be regarded as the proof of the 

 fusion of maxillary and coronoid tentacles is given by the nerve 

 supply. What occurs in the case of the mental and coronoid tentacle 

 of CalUchihys gives a clue as to how the fusion may have actually 

 taken place. Judging from the nerve supply the outer pair of barbels 

 of the Sturgeon are maxillary tentacles. 



The prepalatine piece requires careful observation. In the young 

 Silurus it occurs as a squarish block of cartilage, articulating with the 

 preorbital process. In my specimen of Auchenaspis ossification hud 

 set in around the articulation, and consequently only apophyses of 

 cartilage are left. The anterior block always lies very far forward 

 in the snout. The posterior end serves for the attachment of the 

 adductor muscle proceeding from the ethmoid wall. The muscle is 

 mentioned by Stannius. It works the maxillo-coronoid tentacle. In 

 Trichomycterus a small cartilage remains in the posterior part of the 

 articulation, and on comparing closely the sections of the young 

 Callichthys^ I found that a small projection of cartilage from the 

 skull represented this free cartilage of Trichomycterus. Thus we have 

 a stage when the prepalatine cartilage is continuous with the skull 

 cartilage (the spot is marked with an asterisk in Fig. 7). 



In all Siluroids, this prepalatine piece never enters into conti- 

 nuity with the pterygoid cartilage, the latter being attached by liga- 

 ment to the vomer. The lateral velar supi)orts which may , as in 



