1936] Schults: Keys to Fishes 203 



Ganoid. Scales or plates of bone covered by enamel. 



Gape. Opening of the mouth. 



Geniculate. Having knee-like bends or joints or protuberances. 



Gibbous. Sharply convex or rounded. 



Gill arches. The bony arches to which the gills are attached. 



Gill membranes. The thin wall of skin, supported by the branchios- 

 tegals, and closing the gill cavity below. 



Gill membranes free from the isthmus. Not connected to the isth- 

 mus so that a needle can be run across the isthmus and under 

 the membranes if the right and left sides are connected. 



Gill openings. Opening leading to or from the branchiae or gills. 



Gill rakers. A series of bony appendages, variously placed along the 

 anterior edges of the gill arches. The gill rakers are counted 

 on the first gill arch only, unless otherwise specified. The num- 

 ber of rakers is counted both above and below the angle or 

 bend of the gill-arch, the upper number being mentioned first. 

 All rudiments are counted. The formula, 15 + 25, for exam- 

 ple, indicates 15 rakers on the upper and 25 on the lower limb. 



Gill slit. The openings between the gill arches. The "slit behind the 

 4th gill arch" may be pore-like, absent, or a small slit. If pore- 

 like it is a tiny round opening like the letter "o", but if a small 

 slit, it is a small elongate opening. In both cases this opening 

 is very close to the bony arch and not in the loose membran- 

 eous tissue behind the 4th arch. 



Gills. Organs for breathing the air contained in water. 



Glabrous. Smooth. 



GlossoJiyal. The tongue bone. 



Graduated spines. Progressively longer backward, the third ele- 

 ment being as much longer than the second as the second is 

 longer than the first, etc. 



Granulated. Rough with small prominences. 



Gnlar. Pertaining to the gula, in fishes the region between the chin 

 and isthmus. 



Gidar plate. A single hard plate or plates between the dentary bones 

 of the lower jaw. 



Haemal arch. An arch between the haemal spines, for the passage 

 of blood vessels. 



Haemal canal. The series of haemal arches as a whole. 



Haemal spine. The ventral spine of a caudal vertebra in fishes. 



Head length. Usually called "head" in descriptions. The length of 

 the head is measured from the tip of the snout to the extreme 

 hinder margin of the bony portions of the opercle. It includes 

 the opercular spines in percoid fishes, etc., and the opercular 

 membrane in most fishes. 



