On the Classificalion of Fishes. 279 



In the third order is placed those having purse-shaped gills, fixed 

 and opening outwards, with a circular mouth, and is called 

 Cyclostomi, from kuklos, a circle, and stoma, a mouth ; this 

 order may be studied in the Lampreys, PEXROMYzoNTiDiE. 



The different orders are divided into families ; the families are 

 again divided into genera, and each genus comprises one or mor« 

 species. The order Acanthopterygii, or spine-rayed fishes, is 

 divided now into perhaps twenty different families ; of these the 

 first is the Percid^, the Perch family, so named because th® 

 Perch may be considered as the type of all the fishes included in 

 this family. This family includes a large number of genera, 

 several of which may be met with in our waters. Of these 

 perhaps the genus Perca is the most widely disseminated in our 

 lakes and streams, though it has but one species in x\merica, the 

 Yellow Perch, Perca flavescens. Dekay, in the Natural History 

 of New York, has described five different species, relying on the 

 authority of Cuvier ; but Agassiz says that the differences upon 

 which they are based are not constant characters, and that after 

 comparing specimens from Sault St. Mary, Lake Huron, the waters 

 of Massachusetts, New York and Pennsylvania, he has seen the 

 iame variations occuring in each of the supposed species, anrl 

 is satisfied of their specific identity. The Yellow Perch has 

 two dorsal fins, barely separate from each other, about three- 

 tenths of an inch ; the first has thirteen spinous rays, the second 

 has the first two spinous, and fifteen soft rays. There are 

 fifteen soft rays in the pectoral, and one spinous and five soft rays 

 in the ventrals ; the anal fin has two spinous and eight soft rays, 

 *nd the caudal seventeen soft rays. The number of the fin rays 

 is often stated in scientific works in a brief formula, and those of 

 the Perch would be given thus, D. 13, H, 16 ; P.15 ; V. I, 5 ; A. 

 11,8; C. 17. The rays which support the membrane lying 

 beneath the gill-covers are called the Branchiostegous rays, and 

 ia the Yellow Perch are seven in number. On the side the color 

 is yellow, though varying much in brilliancy in different waters, 

 with several dark vertical bands across the back, extending quite 

 ou to the sides ; the pectoral, ventral and anal fins are a bright 

 orange, the dorsals and caudal greenish ; the iris is golden yellow, 

 and the pupil of the eye is black. 



This handsome fish is also very hardy, and can be easily trans- 

 ported from one pond to another, while the sharp spines of his 

 dorsal fin serve as a good defence against the attacks of those fresh 



