ICHTHYOLOGY. 
ral ; the third, pelagian, &c. Willoughby 
formed his system from his observation on 
the anatomy and physiology of fishes ; lie 
was followed by Ray, who fixed a series of 
genera. Artedi, the friend and country- 
man of Linnaeus, has the merit of having 
first traced the outlines of that classification 
of fishes which is now almost generally 
adopted. For, independently of the ceta- 
ceous tribes, which are now generally 
classed with the mammalia, his method con- 
sisted of four orders, viz. 1. The malacotery- 
gian, or those which have soft fins, or fins 
with bony rays, but without spines. 2. The 
acanthopterian, those with spiny fins. 3. 
The brauchiostegeous, corresponding to the 
amphibia nantes of Linnaeus. 4. The chon- 
dropterygian, or those which have not true 
bones, but only cartilages, and the rays of 
whose fins hardly differ from a membrane. 
At first Linnaeus adopted this method en- 
tirely, but he afterwards improved upon it; 
and now, according to his system, the orders 
have been instituted from the situation, 
presence, or absence of the ventral fins. 
1. Such as are entirely destitute of these 
fins, are termed pisces apodes, apodal or 
footless fishes. 2. The jugulates, or jugu- 
lar, are those which have ventral fins, placed 
more forward than the pectoral fins, or 
under the throat. 3. The thoracici, or 
thoracic, include those whose ventral fins 
are placed immediately under the pectoral 
fins, or on the breast. 4. The abdominales, 
or abdominal, comprise those whose ven- 
tral fins are situated behind the pectoral 
fins, or on the abdomen. 5. There still re- 
mains a particular tribe, denominated car- 
tilaginei, which, as their name imports, have 
a cartilaginous instead of a bony skeleton. 
This tr ibe was by Linnaeus separated from 
the rest, on the mistaken idea, that the indi- 
viduals which fcompose it were furnished, 
both with lungs and gills, and should be 
ranked in the class of amphibious animals. 
The genera which pertain to the preced- 
ing orders are determined by the number 
of rays in the branchiostegous membrane, 
the condition of the teeth, the figure of the 
body, and of other remarkable parts. The 
characters of the species are taken chiefly 
from the number of rays in tire fins, which 
differs in the different species. But, as the 
precise enumeration of these rays is some- 
times a matter of difficulty, and, as they are 
likewise subject to variation, it is necessary 
to have recourse to o flier marks, and to 
adopt, as subsidiary characters, the form 
and situation of particular fins, the propor- 
tion of the head to the body, the condition 
of tlie lateral line, the number of the verte- 
brae and ribs, &c. 
Mr. Pennant describes fishes under the 
three great divisions of cetaceous, cartilagi- 
nous, and bony. The latter which is by far 
the most numerous, he subdivides into four 
sections entitled agreeably to the Linnaean 
orders apodal, thoracic, jugular, and abdo- 
minal. 
Ihe shape of the body of fishes is subject 
to considerable varieties. It is said to be 
compressed, when the diameter, from side 
to side, is less than from back to belly; and 
depressed, on the contrary, when the diame- 
ter, from side to side, is greater than from 
back to belly. It is cylindrical, when it is 
circular in the greater part of its length ; 
ensiform, or sword-shaped, when the back 
and belly terminate in a sharp edge, or 
when the body gradually tapers from the 
head to the tail; cultrated, or knife-shaped, 
when the back is somewhat flat, and the 
angle below acute ; carinated, or keel- 
shaped, when the back is rounded, and the 
under part of the belly acute through its 
length ; oblong, when the longitudinal dia- 
meter is -much longer than the transverse; 
oval, when the longitudinal diameter not 
only exceeds the transverse, but the base is 
circular, and the apex more acute ; orbicu- 
lar, when the longitudinal and transverse 
diameters are nearly equal ; lamellated, or 
spear-shaped, when oblong, and attenuated 
at both extremities ; cuneiform, or wed re- 
shaped, when the body gradually flattens 
towards the tail ; conical, when it is cylin- 
drical, and gro ws gradually more slender to- 
wards the tail ; ventricose, when tire belly 
is very prominent ; gibbous, when the back 
presents one or more protuberances ; an- 
nulated, when the body is surrounded by 
rings, or elevated lines ; articulated, when 
it is covered with connected and bony 
plates; trigon, tetragon, pentagon, and 
hexagon, when the sides are plain, with 
three, four, or six longitudinal angles ; if the 
number of these angles exceed six, it is 
termed a polygon. 
The surface of the body of fishes is term- 
ed naked when it is destitute of scales ; 
scaly, when provided with them; smooth, 
when the scales are without angles, furrows, 
roughness, or inequalities ; lubricous, or 
slippery, when invested with a mucous or 
slimy humour ; tuberculated, or rough, 
when covered with prominent warts or 
tubercles ; papillous, when covered with 
fleshy points ; spinous, when the asperities 
