21 



Ceratodus (Fig. 4). Beneath and at the attachment of the 

 operculum in this animal there is found a small cartilage described 

 by Günther and Huxley and by the latter homologized with the 



Fig. 4. 

 H. M. 



VII Op. c. 



Mck 



Fig. 4. 



Sympl. Ce. hy. 



Outline of Ceratodus from Huxley with different interpretation. 



"hyomandibular" of Elasmobranchs though van Wijhe ^) has affirmed 

 with regard to it that it may with equal probability be regarded as 

 the stylohyal (= interhyal). 



Through the kindness of Mr. Hoyle of the Manchester Museum 

 I have been enabled to make a preparation of Ceratodus and it appears 

 to me that inasmuch as this cartilage undoubtedly sup- 

 ports the operculum it must be regarded not as hyomandi- 

 bular or interhyal but as opercular cartilage. 



Then comparing Ceratodus with e. g. the young Silurus described 

 above it will be seen that the cartilage of the upper jaw contains 

 the Teleostean elements, hyomandibular, symplectic, quadrate and ptery- 

 goid, all fused together and with the skull. The hyomandibular nerve 

 runs behind the Suspensorium, though in the autostylic Holocephali it 



1) VAN Wijhe, Visceralskelet und Nerven der Ganoiden in : Nied. Arch. 

 f. Zool., Bd. V, 1882. 



