Vlll 
INTKODUCTION. 
are arranged in ascending series, so far as can be determined, while 
the “ Teleostei ” are treated in precisely the opposite order. 
This dual subdivision may appear, at first sight, to be the logical 
result of Agassiz’s recognition of the primitive nature of the typical 
“ Ganoidei,”—especially when added to Miiller’s subsequent discovery 
of the important characters these fishes possess in common with the 
Elasmobranchs, Chimaeroids, and Dipnoans. A consideration of the 
researches of Agassiz himself, however, suffices to demonstrate that 
if gradations in skeletal anatomy are more or less concomitant, as 
usual, with the evolution of the soft parts, every essential link be¬ 
tween the “ Ganoidei ” and “ Teleostei ” is already known. So long 
ago as 1866, this fact was clearly recognized by Owen 1 , when he 
proposed to group the Ganoids and Teleosteans in a subclass Teleos- 
tomi, adopting the Plagiosxomi (including Holocephali) and Dipnoi 
as equivalent divisions. About the same time, Kner 2 concluded that 
the group of Ganoidei was not homogeneous, and was, at least in part, 
separated too widely from the Teleosteans by Agassiz. The sub¬ 
sequent investigations of Cope 3 , Gill 4 , Liitken 5 , and Huxley 6 have 
tended in the same direction; and the most recent statements of 
the last-named author concerning points of visceral anatomy will be 
generally regarded as final and conclusive. The researches of Doas 
are cited to prove that there is no absolute distinction between 
Ganoids and Teleosteans in the conus arteriosus of the heart; 
the rudiment of a spiral valve in the intestine of Chirocentrus is 
noticed as rendering a second point of the original Mullerian 
diagnosis invalid; while a reference to Wiedersheim’s discovery 
of the partial decussation of the fibres of the optic nerves 
in some lizards, suggests that if this feature be of little syste¬ 
matic importance in an order cf Eeptiles, it is not likely to be 
1 K. Owen, ‘ Anatomy of Vertebrates/ vol. i. (1866), p. 7. 
2 R. Kner, Sitzungsb. k. Akad. Wiss., matk.-naturw. Cl. vol. liv. pt. i. (1866), 
pp. 519-536. 
3 E. D. Cope, Trans. Amer. Phil. Soc., n. s., vol. xiv. (1871), pp. 445-460 ; 
Proc. Amer. Assoc. Adv. Sci. 1871 (1872), pp. 317-343 ; Amer. Nat. vol. xix. 
(1885), pp. 234-243; ibid. vol. xx. (1886), p. 1031 ; ibid. vol. xxi. (1887), 
pp. 1014-1019; ibid. vol. xxiii. (1889), pp. 852-860; Proc. Amer. Phil. Soc. 
1884, pp. 577-585. 
4 T. Grill, Proc. Acad. Nat. Sci. Philad. 1861, pp. 12-20 ; and “ Arrangement 
of the Families of Fishes,” Smithsonian Miscell. Coll. vol. xi. (1872). 
5 C. Liitken, “ Ueber die Begrenzung und Eintheilung der Ganoiden,” Palas- 
ontographica, vol. xxii. (1873), p. 1; translated from Yidenskab. Meddel. Naturh, 
Foren. Kjobenhavn, 1868. 
6 See especially Proc. Zool. Soc. 1876, pp. 24-59, and ibid. 1883, pp. 137-139. 
