TERMS USED IN DESCRIPTION. 759 
with membrane bones (opercula, etc.) in connection with it, and contain- 
ing a brain of several differentiated ganglia; shoulder girdle developed, 
lyriform or furcula shaped; a distinct lower jaw; branchis, with the 
outer edge free, attached to about five bony arches, which are connected 
with the hyoid bone and parallel with the shoulder girdle, the hinder- 
most pair modified into tooth-bearing “ pharyngeals;” gill openings a 
single cleft on each side behind the operculum, either confluent below 
or else separated by an isthmus; heart (typically) with two cavities and 
an arterial bulb. In most fishes there is a membranous air bladder 
lying immediately beneath the back bone, answering homologically to 
the lungs of the higher vertebrates. In a few Ganoids the air bladder is 
cellular and more or less functional, and connected by a glottis with the 
cesophagus; in most of the soft-rayed species (Suckers, Minnows, Sal- 
mon, Catfishes, etc.) there is a slender duct connecting the air bladder 
with the alimentary canal; in the spinous fishes (Perch, etc.) this is 
wanting. Reproduction by eggs of small size, which are usually fertil- 
ized after exclusion; the members of a few groups (Cyprinodontidx, Am- 
blyopsidz, etc.) are ovoviviparous, the young being developed in a sort of 
uterus. (Latin piscis, a fish.) 
Nore.—The terms used in the description of fishes may perhaps best be made clear to 
one not familiar with them by a sort of object lesson. The reader is supposed to have 
at hand a specimen of the Common Brook Sucker (Catostomus teres) and a Black Bass 
(Micropterus salmoides). The general form of the body is, in this memoir, usually first 
indicated in general terms, as elongate, oblong, short, deep, etc.; more specific terms are 
compressed (flattened laterally); depressed (flattened from above); fusiform (spindle- 
shaped, tapering each way from the shoulders); terete (nearly cylindrical, 4. e., the ver- 
tical and horizontal diameters about equal. The depth of the body is described by com- 
parison with the length, along the side from the tip of the snout to the base of the caudal 
fin. The depth is measured at the deepest point, and is proportionately greater in old 
fishes than in young. The general form of the head is next noted; then the form and 
position of the mouth; the mouth is terminal when its opening is forwards, and the two 
jaws are not very unequal in length, as in the Black Bass ; it is inferior, when, by the 
shortness of the lower jaw, its position is entirely underneath the snout, as in the 
Sucker; it is oblique when its cleft slants backward and downward when the mouth 
is closed; it is horizontal when the reverse is the case. The bones of which the jaw is 
composed are the following: The two dentary bones joined by a symphysis in front, form- 
ing the mandible or lower jaw; the pre-mawxillaries, or inter-maxillaries, forming always the 
middle of the front part of the upper jaw, 2ad in some cases forming its entire edge, as 
is the case in the Black Bass. Attached to the pre-maxillaries, either behind them, 
as in the Black Bass, or below them, asin the case of the Trout, are the mazillaries or su- 
pra-maxillaries. In the Black Bass these are conspicuous and flat, extending back below 
the eye; in the Sucker they are hardly recognizable without dissection; in some fishes 
there is attached to the upper posterior edge of the maxillaries and parallel with it a 
very small bone called the supplemental mawillary. The relative size of the mouth is 
conveniently indicated by describing how far back the maxillary extends; thus ‘ max- 
