Prof. E. D. Cope on the Systematic Relations of Fishes. 159 



(Parker, mastoid of Cuvler and Owen) is characteristic of 

 bony fishes. 



The types of variation in the first point, only distinguish 

 groups of subordinate rank. Thus tlie suspensor of the 

 mandible in the typical fishes consists of the hyomandibular 

 stapes, quadrate (metapterygoid or incus), syraplectic, and 

 mesopterygoid {quadrato-jugal^ Miiller; quadrate^ Huxley, 

 Elem. Comp. Anat.). In the Mormyrida3, Silurid^, Poly- 

 pterida?, and others, the symplectic is absent ; in the Eels of 

 several families both it and the metapterygoid are wanting, 

 reducing the suspensorium to a rod of two pieces. This con- 

 dition exists in many of the Rays ; in others and in the Sharks 

 the inferior element is wanting (Miiller, Stannius). An 

 important modification is exhibited by Chimcera, where the 

 hyomandibular, which alone exists, is continuous with the 

 cartilaginous cranium, not being separated by the usual arti- 

 culation. 



As to the opercular bones, all are wanting in the Elasmo- 

 branchs (Sharks and Rays), while the typical fishes possess 

 four, viz. preeoperculum, operculum, suboperculum, and inter- 

 operculum. In many of these, however, the suboperculum is 

 wanting ; and in the Sturgeons and many Eels there is no 

 praioperculum. In Polyodon the interoperculum is also want- 

 ing. In Lejyidosiren the operculum and interoperculum are 

 rudimental. In respect of this point also, the divisions indi- 

 cated are of subordinate value. As regards the development 

 of the pterotic bone, its history is not yet sufficiently made 

 out to enable us to understand its value. It does not exist in 

 those with cartilaginous cranium (Elasmobranchii). The 

 Elasmobranchs are well known to have the scapular arch 

 suspended freely behind the cranium, as in higher Vertebrates. 

 It is not always attached to the cranium, on the other hand, 

 among true fishes 5 for in the Eels it is quite as in the Sharks, 

 and the spinous-finned Mastacemhelus presents the same 

 features. 



The characters presented by the pelvic bones and limbs seem 

 to be of higher import. Thus all the bony fishes and Sturgeons 

 lack all the pelvic elements. In the Sharks and Rays they 

 are also wanting ; but two elements on each side appear in the 

 Holocephali ( Ghimcera) according to Leydig and Gegenbaur. 

 In Lepidosiren a large median pelvic cartilage exists ; but 

 which element it represents is unknown. This is evidently a 

 character of high significance. As to the limbs, the pecu- 

 liarities of Polypterus have been pointed out above. They 

 mean nothing less than the development of the elements of the 

 arm and leg of the higher Vertebrata which intervene between 



