CXXxiv FISHES OF ILLINOIS 



GUI-membranes. The thin wall of Bkin, supported by the branchiostegals, and closing the gill- 

 cavity below. (Fig. 8 and 9.) 

 Gill-rakers. A series of tooth- or filament-like bony appendages placed along the anterior edge 



of the first gill arches. (Fig. 2, gr.) 

 Graduated. Becoming progressively longer in one direction. Said of the spines in the fins of 



certain fishes. 

 Gular plate. A bony plate imbedded in the skin between the sides of the lower jaw of certain 



ganoid fishes. 

 Hcemal spine. The lower spine of a caudal vertebra. 

 Heterocercal. Unequally lobed. Said of the tail of a fish in which the vertebral column is bent 



upward posteriorly. (Fig. 4, 5, and 6. See also note under c, of key to families, p. 1.) 

 Homocercal. Equally lobed. Said of the tail when the backbone stops (at least apparently) 



at the middle of the base of the caudal fin. (Fig. 7. See heterocercal.) 

 Hyoid. A bone in the floor of the mouth; tongue bone. (Fig. 57, hy.) 

 Hyomandibular. One of the chain of bones forming the suspensorium of the lower jaw (i. e., 



connecting it with the skull). 

 Hypercoracoid. An element of the shoulder girdle. 

 Hypocoracoid. An element of the shoulder girdle. 

 Hypural. The expanded last vertebra. 

 Imbricated. Overlapping, like shingles on a roof. 



Infraoral. Below the mouth. Said of the teeth of the mouth disc below the oesophageal open- 

 ing in lampreys. (Fig. 10.) 

 Infraorbitals. A chain of small bones below the eye. 

 Interneurals. The bones to which the dorsal fin rays are attached. 

 Interopercle. A bone of the lower part of side of head. (Fig. 1, io.) 

 Interorbital space. The space between the eyes on top of the head. 



Isocercal. With the vertebrae becoming progressively smaller backward, as in the codfishes. 

 Isospondylous. With the anterior vertebrae simple. Said of the herring- and pike-like fishes, 

 which lack the Weberian ossicles found in the suckers, carps, and catfishes. (See Weberian 

 ossicles.) 

 Isthmus. The fleshy interspace between the gill-openings. 

 Jugular. Pertaining to the throat. Said of the ventral fins or vent when placed in advance of 



the attachment of the pectorals. 

 Keeled. (See carinate.) 



Larva. The young of an animal, if differing in an important way from the adult. 

 Lateral line. A series of sensory muciferous tubes along the sides of a fish. 

 Leptocephalus. A name applied to the larval form of the eel. 

 Lingual. Pertaining to the tongue. 

 Lingual teeth. The serrated teeth on the "tongue" (i. e., at the opening of the esophagus) in 



lampreys. (Fig. 10.) 

 Lunate. With a broad and shallow notch. 

 Mandible. The lower jaw. (Fig. 1, md.) 



Maxillary. The posterior element of the lower jaw. (Fig. 1, mx.) 

 Metapterygoid. One of the chain of bones connecting the lower jaw with the skull. 

 Molar. With a flattened, grinding surface. Said of teeth. 

 Muciferous. Producing or containing mucus. 

 Muscular impressions. The visible diagonal lines or grooves marking externally the intervale 



between the muscle plates. (See myotome.) 

 Muzzle. The anterior extremity of the head. 

 Myotome. A muscle plate. (See muscular impressions.) 

 Nape. The part of the neck next to the occiput. (Fig. 1, np.) 

 Nasal. A bone of the nose. 

 Neural spine. The upper spine of a vertebra. 



