222 FISHES OF ILLINOIS 



much like the mucin secreted by the vineyard 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 open- 

 ings, 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 pugna- 

 cious male watches the nest and w^ards 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 

 inedian 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 lanceo- 

 late plate with a single strong median carina. Fresh waters of North 

 America; one species known. 



EUCALIA INCONSTANS (Kirtland) 

 (brook stickleback) 



Kirtland, 1841, Bost. Joum. Nat. Hist., Ill, 27.5 (Gasterosteus). 

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

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



Length 2 J inches; body rather deep and moderately compressed; 

 caudal peduncle rather stout and not keeled; depth 3.8 to 4.4; greatest 

 width about f 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-Hke bands more or less 

 confluent in ring-like pattern; lower parts silverv^; upper part of cheek 



*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," Vol. II., p. 230. 



