RELATIONS OF ANTERIOR VISCERAL ARCHES. 63 



the bottom of the column ; progressive stages of skull structure are 

 represented in the middle and right-hand columns. The cranial 

 plan of Ceratodus is regarded as representing the ancestral condi- 

 tion of both Cestracion and the Ganoids. Cestracion, classed with 

 Notidanus as an amphistyjic type, is regarded also as transitional, 

 a low form of the hyostylic type. 1 The diagram confirms the 

 inference that Huxley conceived the palatoquadrate as originally 

 a part of the skull, which gradually became constricted off as in 

 Ceratodus and finally freed from it entirely as in Raia and the 

 Teleosts. 



Wiedersheim (Parker s translation, '97). 



" The palatoquadrate is usually only united to the basis cranii by liga- 

 ments, but in the Chimteroids. . . it becomes immovably fused with it, 

 whence their name of Holocephali. In the Sharks and Rays the palato- 

 quadrate is not directly united to the skull, but is suspended from it by the 

 hyomandibiclar. ... In this case the skull may be described as hyostylic, 

 to distinguish it from autostylic skulls, in which the hyoid takes no part in 

 the suspensodum " (op. cit., p. 75). 



Comments: (i) "Hyoid" here refers to the hyoidean arch, 

 not to the hyoid or ceratohyal. (2) In general it would be less 

 confusing to say that it is the mandible rather than the palato- 

 quadrate which is suspended from the hyomandibular, and that 

 the palatoquadrate rests chiefly upon and is fastened to the 

 mandible. 



v. Zittel, 1903 (Eastman's edition). - 



" In the Holocephali the palatoquadrate and hyomandibular fuse together 

 and with the cranial capsule. The mandible thus becomes autostylic, i. e., 

 articulates directly with the cranium" (op. cit., p. 11). 



Comments : (i) The statement in regard to the hyomandibular 

 seems incorrect. In a specimen of Chimcera collei kindly loaned 

 to me by Professor Bashford Dean the hyomandibular is seen to 

 be a large independent element (see Fig. 11) serially homolo- 

 gous with the epibranchials as in Selachii, and tipped with a 

 reduced pharyngohyal, both being free from the chondrocranium. 

 (2) To apply the term autostylic to the mandible is to introduce 

 a new element of confusion in a matter already sufficiently 

 complicated. 



1 On page 43 of Huxley's memoir the Cestracion skull is referred to as a low form 

 of " autostylic type," but examination of the context and of the diagram cited show 

 that this is probably a misprint for " hyostylic." 



