1884.J 579 [Cope. 



brain. But it is singular that no one, so- far as I know, has insisted upon 

 the fact, not only that the Teleostean brain is essentially similar to that of 

 the Ganoids, but that it is exactly in those respects in which the Ganoids 

 and Teleostei agree in cerebral structure that they differ most markedly 

 from the Plagiostomi and Chimeeroidei. ^~- 



"With respect to the chiasma of the optic nerves, the exact nature of 

 that structure has not yet been properly elucidated either in the Selachians 

 or in the Ganoids. But, whatever may come of such an investigation, 

 the establishment of the existence of a true chiasma in the Ganoids, and 

 of its absence in Teleosteans, can have but little bearing on the question 

 of their affinities, since Wiedersheim has shown that a simple decussation 

 of the fibres of the optic nerves, as in ordinary Teleosteans, takes place in 

 many lizards." 



In 1877* I proposed the following primary divisions of the fishes, and 

 have seen no reason to alter my views as to their value as a correct ex- 

 pression of the affinities and diversities of this class of Vertebrata. The 

 system differs only from that of 1871 in the consolidation of the Crossop- 

 terygia and Actinopteri into a single sub-class, the Hyopomata ; and in a 

 few corrections of the definitions given. They are as follows : 



I. Suspensorium continuous with the cartilaginous cranium, with no 



hyomandibular. No rudimental opercular bone ; no maxillary arch ; 

 pelvic bones present ; axial series of fore limb shortened, the deriva- 

 tive radii sessile on the basal pieces ; axial series of hinder limb pro- 

 longed in male HolocepTiali. 



II. Suspensorium articulated with the cranium ; no maxillary arch ; no 

 opercular nor pelvic bones ; bones of limbs as in the last 



ElasmobrancJii. 



III. Suspensorium rudimental, continuous with cranium, supporting one 

 or more opercular bones ; cranium with superior membrane bones ; 

 no maxillary arch ; a median pelvic element ; the limbs supported by 

 segmented unmodified axes Dipnoi. 



IV. Hyomandibular and palatoquadrate bones articulated with cranium, 

 supporting opercular bones ; a maxillary arch ; no pelvic element ; 

 axes of the limbs shortened, the derivative radii sessile on the basal 

 pieces Hyopomata. 



In the definition of the Dipnoi, it is necessary to make the correction in 

 accordance with the best observations on fresh specimens, above referred 

 to, as I have not been able to determine the question from dried speci- 

 mens in the Hyrtl collection. The suspensorium cannot be properly said 

 to be articulated to the cranium in the sense in which it is said to be such 

 in the Elasmobranchi. In the latter it is articulated by ginglymus ; in 



•■"Proceedings of the American Philosophical Society, 1S77, p. 25; and in the 

 Annual Reports of the Commissioners of Fisheries of Pennsylvania for 1879-80, 

 p. 67 and 1881-2, p. 111. 



