42 



DR. W. G, RIDEWOOD OX THE CRANIAL 



[May 3, 



basibranchials is roughly hexagonal in shape, elongated in an 

 antero-posterior direction, and continued posterioi-ly into a small 

 rod of cai'tilnge which lies fi-eely between the fifth cerato- 

 bi-anchials. 



The dentigerous plates on the fifth ceratobranchials are readily 

 removable, which is not usually the case. There is a true ossified 

 first pharyngobranchial, projecting slightly upwards by the side of 

 the pai-asphenoid, in addition to the small spicular bone, which in 

 Teleosteans generally has been ei-roneously taken to represent the 

 first pharyngobranchial. The spicular bone stands upright from 

 the antero- superior extremity of the first epibranchial, and serves 



Text-fig. 11. 



eM 



ISlops saurus, hyobrancliial skeleton, dorsiil view. The epibvaucliials and 

 pharyngobrancliials of tlie right side are not shown. For explanation ot 

 lettering, see p. 81. 



to attach the branchial skeleton to the pro-otic bone at the point 

 where the latter meets the opisthotic bone. The fourth pharyngo- 

 branchial is cartilaginous, and is flanked on its phaiyngeal surface 

 by a dentigerovis membrane-bone exactly similar to those which 

 occur on the second and third pharyngobrancliials. Even the first 

 pharyngobranchial bears a small dentigerous plate in its posterior 

 part. The transition from these dentigerous plates to the small 

 toothed plates that accompany the gill-rakers on the epibianchials 

 is quite gradual. The whole hyobranchial skeleton gives one the 

 impression that it is in a veiy simple and unmodified condition. 



