MORPHOLOGY OF TELEOSTEAN HEAD SKELETON. 555 



though the palatine is small it possesses a inoderately 

 developed process and is beset with teeth, thereby showing 

 that the absence of these features in all the other forms 

 possessing this type of palato-ethmoidal relationship is by no 

 means an essential accompaniment of it. 



Among Acanthopterygii the Zanclidae and AcronuridaB, 

 whose position is by no means a settled question, are character- 

 ised by the possession of this type of palato-ethmoid relation. 



In Zanclus cornutus (fig. 52) the small palatine {pa.) has 

 an insignificant maxillary process behind, which is the facet 

 for the pre-palatine articulation. The ethmoid region is of 

 the type usually associated with the possession of this single 

 articulation, and its shape as a whole calls to mind that of 

 young Siphonostoma (fig. 48) and is still largely cartilaginous 

 anteriorly. 



The Acanthurus coruleus (one of the Acronuridre) 

 presents a condition so closely similar to that of Balistes 

 maculatus (fig. 53) that a description of the latter — a Plecto- 

 gnath — will do service for both. Its palatine has the same 

 relations as that of Zauclus. The ethmoid region is not so 

 long, but is nnicli more massive. In my specimen the pre- 

 ethmoid cornu, with its well-defined articular surface {'pn.'), 

 is still cartilaginous, and is bounded beneath by the vomer 

 and above by the mesethmoid bone. There is no trace either 

 of rostrum or of post-palatine articulation. Klein, when 

 describing the ethmoid region of Acanthurus (Teuthis ; 84, 

 pp. 187, 219) and Balistina (ibid., pp. 190, 237), called atten- 

 tion to the close resemblance between them. 



Thus all the Scomberesocidae, Hemibranchii, Lopho- 

 branchii, Plectognathi, and among Acanthopterygii, the 

 Zanclidas and Acronuridfe, are characterised by the pos- 

 session of only one palato-ethmoidal connection, viz. the 

 pre-palatine, and of an ethmoid region with its pre-ethmoid 

 cornua carried at the extremity. 



The majority of these forms are characterised by the great 

 elongation of the ethmoid region and by the shortness of the 

 mandible, thus suggesting a possibility that the post-palatiue 



