Fist Hs: 
A fish in the popular sense of the word is a member of any one of the 
four classes of aquatic or fish-like vertebrates, the Pisces (True Fishes), the 
Elasmobranchit (Sharks, Skates, etc.), the Marsipobranchit (Lampreys), and 
Leptocardy (Lancelets). <A fish in this comprehensive and rather in- 
definite sense may be defined asa cold-blooded vertebrate, adapted for life 
in the water, breathing by means of gills, the limbs if present developed 
a fins, the fingers and toes being represented by cartilaginous rays con- 
nected by membrane, the exoskeleton obsolete or developed as scales or 
bony plates, and one or more fins developed on the median line of the 
body, usually composed of rays connected by membrane. 
Of a fish, in the popular sense, one could hardly say more, without the 
necessity of the constant introduction of exceptions. Of a “true fish, 2.e., 
a member of the Class Pisces, a definition will be given further on. 
Of the four classes of fish-like vertebrates only two are represented in 
the waters of Ohio. These are the Lampreys (Harstpobranchit) and the 
True Fishes (Pisces). These two may be compared. as follows: 
* Skull imperfectly developed, without lower jaw or membrane bones (opercula, etc.); 
paired fins (pectorals and ventrals) undeveloped, with no shoulder girdle or pelvic 
elements; gills purse-shape, usually with several external openings ; nostril single, on 
the median line of the head ; body ec!-shaped, scaleless. . . . MARSIPOBRANCHII. 
** Skull well-developed, with a lov -: jaw and membrane bones; paired fins more or 
less developed, with a shoulder girdle (:)riform or fureula-shaped) curved forwards and 
with its respective sides connected below; and with distinet pelvic elements ; gills not 
purse-shaped, their external openings single on each side; nostrils one on each side, 
their openings often double; body variously formed, usually scaly. . . . PISCES, 
Beginning with the lowest, or least complicated of these groups we come now to the 
consideration of 
CLASS I. MARSIPOBRANCHIL. THE MYZONTS. _ 
Skeleton cartilaginous; the skull inperfectly developed, not separate 
from the vertebral column ; noribs; notrue jaws; nolimbs; no shoulder 
girdle nor pelvic elements; gills in the form of fixed sacs, without 
branchial arches, six or seven in number on each side; a single nasal 
aperture; mouth subinferior, nearly circular, adapted for sucking ; heart 
