Oiiiida Lake fishes 281 



Head in length. The distance from the snout along the cheeks to the extremity 



of the opercles as contained in the distance from the snout to the base of 



the caudal fin. 

 Height. As applied to a fin, it is usually the length of its longest ray. 

 Hetcrocercal tail. Tail with the backbone prolonged dorsally into the upper lobe 



of the caudal fin. This lobe of the fin is usually more highly developed than 



the iowiT. but in .linia the difference is not marked. 

 Hyoid bones. Bones in the floor of the mouth, supporting the tongue. 

 Inferior mouth. Mouth decidedly on the under side of the head, opening 



downward. 

 Interspinals. Bones to which the rays of the fins are attached. 

 Isthmus. The narrow bar in the floor of the phar>nx, separating the gill chambers. 



Fig. 179. 

 Lateral band. A horizontal pigmented band along the sides of a fish. 

 Lateral line. .\ line of sensorj- organs along each side of the body. Fig. 179. 

 Length. The length of a fish is considered to be from the tip of the snout to the 



posterior end of the vertebral column. The total length, however, is from 



the end of the snout to the tip of the caudal fin. The length of a fin is 



taken along its base. 

 Mandible. Lower jaw. 

 Ma-villary bones. Bones attached to the prema.xillaries laterally; sometimes lying 



alongside the premaxillaries as in the Rock Bass (Fig. 179), or continuous 



with them as in the catfish (Fig. 180). 

 Naked, .\pplied to the \wA\ when scales or other dermal mcnlifications are absent. 

 Nape. Region just behind the occiput. 

 Nostrils. Openings of the nasal ch.imbers. Fig. 179. 

 2\'uptial tubereles. Outgrowths on head or body in the fonn of granules or 



denticles that api>car in breerling male fish. Called also [x-arl organs. 

 Oceiput. Posterior dor.-ial i»rt of the head or skull. Fig. 179. 

 Opereles. The same as the gill covers. Fig. 179. 

 Opercular bone. The flat, more or less triangular bone supporting the gill cover 



or opcrcle. 

 Operculum. The same as the gill cover or opcrcle. 

 Opercular flap. \ jKislerior prolongation of the operclc. usually colored differently 



from the rest. Found in sunfishes. Fig. 179. 

 Oral 7'alzrs. Thin, membranous flaps used in breathing ; jtist inside the mouth 



opening on l>oih upper and lower jaws. 

 Orbit. Cavity of the skull containing the eye. 



Palatines. Bones just back of the vomer in the roof of the mouth, one on each side. 

 Papillae. Small roundish, fleshy projections, as on the lips of some suckers. 

 Papillose. Co\err<l with papillae. 



Parietals. Bones of the siclcs of the skull. al>ove and just !«ck of the eyes. 

 Pearl organs. Hard tul>erclcs or grantiles developing on breeding male suckers and 



minnows. Called also nuptial tulx-rclcs. 

 Pectoral arch. A Imimv framework UMially conncctcti with the skull an. I ^ni>i>i>rtiin: 



the pectoral fins. 



