THE LIMITS OF THE CLASS OF FISHES. 75 
2d class; Fishes proper with two orders, Ctenoids and Cycloids. 
3d class; Ganoids with three orders, Celacanths, Acipense- 
roids, and Sauroids; and, doubtful, the Siluroids, Plectognaths 
and Lophobranches. 
4th pp — with their orders, Chimera, Galeodes, 
and Batides 
The goeie and Dipnoans were not referred to in this 
essay and consequently it is doubtful what the author considered 
to be their relations. 
In 1866, Prof. Häckel also divided the fishes into four classes, 
but on entirely different grounds and with extremely different limits 
from those proposed by Prof. Agassiz; the classes recognized by 
Häckel being represented severally by (1)Branchiostoma (Lepto- 
cardia), (2) the Myxinoids and Petromyzontes (Cyclostoma) and 
(3) all other fishes (Pisces) except Protoptera, which (4) consti- 
tutes a fourth class (Dipneusta). Hackel, moreover, does not con- 
sider the fishes as a group coördinate with any combination of other 
vertebrate classes; contrasting the Leptocardia in a group (Sub- 
phylum Leptocardia or Acrania) opposed to all the rest of the ver- 
tebrates (Subphylum Pachycardia or Craniota); and under the 
latter opposing the (1) Cyclostoma in a “ cladus” or superclass 
Hauptklasse Monorrhina), coérdinate with (2) another (Anamnia) 
containing the fishes, ‘* Dipneusta,” “ Halisauria” (extinct swim- 
ming reptiles), and Batrachians, and (3) a third (Amniota) 
embracing reptiles, birds and mammals. t 
In 1868, Prof. Cope, t in a suggestive article on the doctrine of 
evolution, considered the Leptocardii, Dermopteri, Elasmobranchii, 
Teleostei (including Ganoidei as a subclass) and Dipnoi to be 
groups coérdinate with the Batrachia, Reptilia, Aves and Mam- 
malia and therefore classes :§ in a subsequent memoir, he reiter- 
ates more distinctly the same opinion, remarking that ‘‘ The classes 
Aves, Reptilia, and Batrachia are those over which the present 
review extends. The classes of vertebrata not included are: the 
Wat Irr: 43 yT, A Orat CA 
* Agassiz (Louis). C ti 
ca, I, path . 187 (Essay on classification, chap. iii, section i Di , 
t Hack Taki: Generelle Morphologie der — a b. 2 sro Entwick- 
aai der Organismen), 1866, pp. € Natürliche Schöp- 
fungs geschichte (1868), 2e. anfl. 1870, pp- rete ge 
Boe 708 PE (Edward Drinker). panel thé Origin n of Genera . . . . < Proceedings of the 
1 256-265. 
§ The groups in question are arran : n the same varies line in five tables exhib- 
iting anat omii ical d details i in which the subordination n of groups groups appears to have been 
: efully 
