222 FISHES OF ILLINOIS 



kidney, is much like the mucin secreted by the vinej^ard snail, 

 Helix pomatia. The nest is built, by the exertions of the male 

 alone, among the stems of aquatic plants where there is some 

 current.* It has two openings, which are ''as smooth and 

 symmetrical as the hole leading into a wren's nest, and not 

 unlike it. " The male induces the female to enter the nest and 

 lay her eggs, after which he enters and deposits his milt. The 

 holes in the nest are in the direction of the current, so that a 

 stream of water passes through it continually. The pugnacious 

 male watches the nest and wards off all intruders. 



Key to the Genera of GASTEROSTEID^ found in Illinois 



a. Pubic bones firmly united, forming a lanceolate plate with a single strong 

 median keel; tail without keel, deeper than broad; dorsal spines 4 or 5, 

 the spines in a right line, non-divergent Eucalia. 



aa. Pubic bones weak and feebly united to form an elongate plate with a 

 median longitudinal groove, on each side of which is a raised edge; tail 

 broader than deep, with lateral bony keel; dorsal spines 8 to 11, divergent 

 from right to left at various angles Pygosteus. 



Genus EUCALIA Jordan 



FIVE-SPINED sticklebacks 



Sticklebacks of typical form, feebly armed, the skin not mailed, and the 

 dorsal spines few (not more than 5) and non-divergent; tail deeper than 

 broad, without keel; pubic bones firmly united, forming a lanceolate plate 

 with a single strong median carina. Fresh waters of North America; one 

 species known. 



EUCALIA INCONSTANS (Kirtland) 



BROOK STICKLEBACK 



(Pl., p. 220) 



Kirtland, 1841, Bost. Journ. Nat. Hist., Ill, 273 (Gasterosteus). 



J. & G., 394 (Gasterosteus); M. V., 97: J. & E., I, 744; N., 42 (inconstans and 

 pygmsea); J., 51; F., 70 (Gasterosteus); F. F., I. 6, 68; L., 22. 



T ength 23^2 inches ; body rather deep and moderately compressed ; caudal 

 peduncle rather stout and not keeled; depth 3.8 to 4.4; greatest ^Aidth about 

 % of greatest depth; depth of caudal peduncle 1.8 to 2.9 in its length. Color 

 (females and young) olivaceous, with faint lighter mottlings and with many 

 fine dots of black; upper part of sides and caudal peduncle with about 10 

 dark cross-bar-like bands more or less confluent in ring-like pattern; lower 



* For full description of nest-building of Gasterosteus cataphractus see J. K. Lord as Quoted 

 by Dr. Jordan in "Guide to the Study of Fishes, " Yd. IT. p. 2.''0. 



