April, 1910. Fishes of Chicago — Meek and Hildebraxd. 303 



orbit; snout 4.0 to 5.0 in head; eye 3.2 to 3.4; caudal fin truncate or 

 slightly emarginate. 



Color olivaceous with faint lighter mottlings ; lower parts silvery ; 

 spring males black with some red anteriorly. 



Length 2]^ inches. 



This fish inhabits small streams and brooks from New York to 

 Iowa and the Saskatchewan. 



Genus PygOHteus Brevoort. 

 NiNfE-spi.vED Sticklebacks. 

 Body elongate; no scales; skin with bony plates along bases of 

 dorsal and anal and on caudal keel; dorsal spines 8 or more; tail 

 broader than deep, keeled; pubic bones weak, forming an elongate 

 plate with a median longitudinal groove. 



Pygosteus pungitius (Linnaeus). Nixe-spined Stickleback. 



Head ^.^ to 3.7; depth 5.1 to 5.6; D. ix or x, 9 or 10; A. 1, 8. 



Body elongate, slender; caudal peduncle with a lateral bony keel; 

 mouth larger and less oblique, the maxillary reaching nearly to orbit ; 

 snout 3.3 to 3.8 in head; eye 3; caudal fin rounded or pointed. 



Color olivaceous above, with small spots and irregularly barred 

 with darker; silvery below. 



Length 3 inches. 



This species inhabits northern Europe and northern North America- 



Family PereopNidte. 



The Trout Perches. 

 Body elongate, somewhat compressed ; caudal peduncle long and 

 slender; scales strongly ctenoid; head without scales; lateral line 

 present; anterior vertebrae simple; ventral fins abdominal, of one 

 spine and about 8 soft rays; anal with i or 2 spines; an adipose fin 

 present; gill membranes separate, free from the isthmus; premax- 

 illaries not protractile; stomach siphonal, with about 10 well devel- 

 oped pyloric coeca; air bladder with an open duct; ova large not 

 falling into the abdominal cavity before extrusion. 



Genus Percopsis Agassiz. 

 Body elongate; dorsal spines weak; body quite translucent; 



preopercle not distinctly serrate; teeth present on jaws, small, villi- 

 fomi. 



