CHONDROSTEOUS FISHES. 
1043 
PISCES CHONDROSTEI 
(STURGEON-FISHES). 
Fishes with endoskeleton principally cartilaginous, but with dermal ossifications repre- 
senting several of the internal bones of the Teleosts, with shoulder-girdle suspended from 
the head, with maxillary and palatine arches free from the skull or united therewith 
merely by a mobile connexion, with branchial cavity, which is situated under the skull 
and common to the free branchial arches, more or less entirely covered by the opercula, 
with fully heterocercal caudal fin, and with paired fins unilaterally rayed. Nostrils lateral, 
set just in front of the orbits. 
We have briefly mentioned above (p. 1) the most 
important anatomical points wherein the Teleosts differ 
from other piscine orders, and we have now to examine 
the relations obtaining between those typical fishes 
which in general organization are by no means inferior 
to the Teleosts, but which never attain so high a degree 
of skeletal differentiation or ossification as the latter, 
and have therefore borne the general name of carti- 
laginous fishes. As a rule, though Avith important ex- 
ceptions, Ave find that in these forms the ossification 
deficient in the endoskeleton is compensated in the 
dermal system, Avhich is strengthened or protected Avith 
hard, thick (Ganoid) scales, spiny plates, or scutes. In 
Artedi" they Avere included, together with the Cyclo- 
stomata , in a single order, Chondropterygii, which Avas 
retained under the name of a series by Cuvier 6 , in 
contradistinction to the “true fishes” (Teleosts). Agassiz 
divided this order into two: the Ganoidei c , among 
which he further ranged, on account of their hard 
dermal groAvths, several Teleosts (the Glanoinorphs, 
Plectognates, and Lophobranchs), and the PlacoideC , 
among Avhich he placed the Cyclostome fishes too. 
Bonaparte e introduced the first reform, and removed 
the Cyclostomata to a separate subclass, Marsipobranchii , 
as opposed to the subclass of the Chirmeras, Sharks, 
and Rays, Elasmobranchii, and MulleiC eliminated 
from the order of the Ganoids the said Teleosts. The 
delimitation of the Ganoids from the Teleosts, hoAvever, 
Avas no longer based exclusively either on the enamelled 
scales of the former or on the less advanced calcifica- 
tion (ossification) of their skeleton, but mainly on the 
characters adduced above (p. 1 ) and derived from the 
more intimate fusion (chiasma) of the optic nerves after 
their emergence from the brain, and the prolongation 
of the heart, at the transition to the common branchial 
artery, into a muscular conus arteriosus , furnished in- 
ternally with several roivs of valves. Thus defined the 
Ganoids still comprised, in addition to the Chondrostei, 
the multitude of tishes, possessing more complete jatv- 
bones, but noAv for the most part extinct, in Avhich the 
piscine type has evolved by manifold processes a Avealth 
of forms rivalling that of the Teleosts, but of which 
“ Gen. Pise., p. 64. 
b R'egn. Anim ., ed. 1, tom. II, p. Ill; ed. 2, tom II, p. 128. 
c Rech. Poiss. Foss., tom. II. 
d „ „ „ tom. III. 
e Selacliiorum tabula analytica , Rom® 1839. 
f Abh. Akad. Wiss. Berk 1844, p. 147. 
