55G ICHTHYOLOGY. 



soft and flexible, with the exception, sometimes, of the first ray 

 of the dorsal and pectoral fins. There are also three Sub-or- 

 ders, founded either upon the position of certain fins, or their 

 absence, as (1) the Abdominales, in which the ventral fins are 

 situated far behind the pectorals, as in the Carp, Tench, Bream, 

 Dace, Roach, Pike, Salmon, etc. ; (2) the Sub-brachials, or Sub- 

 brachiati, (terms derived from the Latin sub, under; brachialis, 

 armlet, or brachium, arm,) in which the ventral fins are immedi- 

 ately beneath the pectoral fins or armlets, (or even a little before 

 them,) as in the Codfish, Haddock and Whiting. To this 

 group also belong the Flat-fishes, such as the Plaice, Flounder, 

 Turbot, Sole, etc.; (3) the Apodes, (Gr. footless,) including the 

 Eels, which receive this name from their possessing no ventral fins. 



The other sections of the Osseous division are, (2) Lopho- 

 branchia, (Gr. tuft-gills,) including Bony Fishes which have the 

 gills in tufts, (not pectinated,) and arranged in pairs along the 

 branchial arches ; (3) Plectognathi, those in which the bones of 

 the head are closely combined, including the Gymnodontida or 

 Naked-toothed Fishes, the Balistida, or File-fishes, and the Os- 

 tracionida, or Trunk-fishes. 



The CARTILAGINOUS FISHES are sub-divided (1) into those 

 which have the gills free, Eleutheropomi, (Gr. free-covers or 

 operculce.) The gills in these, are pectinate or comb-like, and there 

 is only a single gill opening. Of these, the Sturgeons furnish 

 an example; (2) those with fixed gills, (Branchiis fixis,) and 

 which have more than one gill opening on each side, including 

 the Sharks, (Squalidce,) the Rays, (Raiidce,) and the Stone-Suck- 

 ers, (Petromyzonidcz,) 



The division Plagiostomi includes those Cartilaginous Fishes 

 which have on the under side of the face, and at a greater or 

 less distance from the extremity, the broad transverse mouth, 

 such as the Sharks and the Rays. The gills in all are fixed 

 with five or six gill-openings. 



The Cyclostomi, (Gr. with circular mouths,) are those Cartila- 

 ginous Fishes which breathe by a "series of cells," the gills 

 not being comb-shaped fringes, but forming sacs or pouches by 

 the union of two opposite ones along their edges. Here are 

 . found the Stone-Suckers, so called because the animal applies its 

 circular lip to the surface of a stone or other solid body in the 

 water, and drawing in the piston-like tongue, produces a vacuum 

 in the mouth, while the pressure of the super-incumbent body 

 of the water causes the lip to adhere to the stone with immense 

 tenacity, until, by the protrusion of the tongue, the vacuum is 

 voluntarily destroyed. 



