32 H. B. POLLARD. 



really becoming free to the exterior, fuses distally with the proximal 

 part of the coronoid tentacle. There is no special root piece. In 

 Silurus the mental tentacle is situated some little way back from the 

 symphysis along the lower jaw, being supported by a plate of pro- 

 cartilage lying just internal to the skin. To this are attached muscles. 

 The condition in Auchenaspis is similar, the basal plate being, however, 

 very much larger. In Auchenaspis there is situated at the outside of 

 the dentary bone a large block of precartilage (Ment. p.) with a 

 posterior ventral projection running parallel with the tentacle as shown 

 in Fig. 2. This block may be a derivative of the tentacle, possibly 

 arising as a bifurcation of the proximal portion. Such a bifurcation 

 is shown in the proximal part of the maxillary tentacle in Tricho- 

 mycterus (Fig. 5, left side of the drawing). 



The outer prong of the bifurcation may have expanded secondarily 

 so as to have formed this great block. The outer mental tentacle of 

 Misgurnus is a continuation from a corresponding block just as if the 

 backward projection of the piece in Auchenaspis were prolonged into a 

 tentacle. A corresponding piece is found in Motella tricirrata, and no 

 doubt in many other Teleostei, in fact this may be in some fish the 

 " Mundwinkelknorpel " of Stanuius. 



A median unpaired mental tentacle is also present in Motella and 

 Gadidae, but it shows few of the characters of atypical mental tentacle. 

 This tentacle is paired in Mullus and Upeneus. 



The lower support of the velum may be a derivative of the mental 

 tentacle though much modified. The mental tentacles of Callichthys 

 show a remarkable similarity with the cartilage in front of the lower 

 jaw of Protoptencs, as figured especially well by Rose and of Ceratodus 

 as figured by Huxley. I have, as in most cases, verified the observa- 

 tions myself, by sections in Protoptems and dissection in Ceratodus. 

 This cartilage however passes under the loAver teeth and is continuous 

 with the Meckelian cartilage showing in this respect no correspondence 

 with Callichthys. The position of this cartilage led Huxley erroneously 

 I think, to term the lower teeth splenial. 



The huge unpaired block of cartilage in front of the lower jaw in 

 Callorhynchus is obviously a mental piece, corresponding to the mental 

 cartilage of Dipnoi (lower labial of Giinther), and somewhat doubtfully 

 to the mental piece of Auchenaspis. In Chimaera as shown by Hubrecht 

 and Vetter it is represented by a small pair of cartilages below the 



