April, 1910. Fishes of Chicago — Meek and Hildebrand. 225 



9. Cheek. 10. Preopercle. 11. Opercle. 12. Subopercle. 13. Spin- 

 ous portion of dorsal fin. 14. Soft portion of dorsal fin. 15. Base 

 of dorsal fin. 16. Pectoral fin. 17. Anal fin. 18. Ventral fin. 19. 

 Base of caudal fin (last vertebra). 20. Caudal fin. 21. Lateral line. 

 22. Depth of the fish. 23. Depth of caudal peduncle. 24. Caudal 

 peduncle. 



The PROFILE of the fish, unless otherwise mentioned, is the curve 

 from the highest point on the back to the tip of the snout. The ori- 

 gin of the DORSAL or anal fin is the insertion of its first spine or ray. 



Fishes in general, and especially those treated of in this paper, 

 breathe by means of gills, which are fine, hair-like projections 

 (branchy), usually supported on the outer curves by cartilaginous 

 or bony arches known as gill arches; in the true fishes, the normal 

 number on each side is four. The gill rakers are a series of bony 

 appendages variously formed along the inner edge of the anterior 

 gill arch. 



The gill membranes usually serve to attach the gill covers 

 to the ISTHMUS, which is the thick, fleshy projection between the gill 

 openings. The branchiostegal membranes are attached to the 

 lower posterior portions of the gill covers; the cartilaginous or bony' 

 supports of this membrane are the branchiostegal rays. 



The pharyngeal bones are behind the gills and at the beginning 

 of the CESOPHAGUS; in the true fishes, they represent a fifth gill arch. 



The fins of fishes are composed of spines .and rays, the former 

 being stiff, bony structures usually connected by a thin membrane; 

 the rays are rather weak, jointed, cartilaginous structures, and are 

 also connected by a thin membrane. 



A cycloid scale has its posterior margin smooth; such scales 

 are usually found on soft-rayed fishes. A ctenoid scale has its pos- 

 terior margin rough or toothed; such scales are characteristic of the 

 spiny-rayed fishes. 



The length of the body of the fish is measured from the tip of the 

 upper jaw to the base of the caudal fin or end of the last vertebra; the 

 total length, from the extreme ends of the fish. The length of 

 the head is measured from tip of upper jaw to the posterior edge of 

 the opercle; the length of the snout, from tip of upper jaw to an- 

 terior margin of the orbit. The depth of the body is measured at its 

 deepest part, none of the fins being included; the depth of caudal 

 peduncle is measured at its narrowest part, its length from base of 

 last anal ray to end of last vertebra. 



The 'scales in the lateral series are counted from upper edge 



