AMBLYOPSID^E THE BLINDFISHES 



217 



jointly with the less abundant species, F. dispar, with one and 

 a third times that frequency facts which are to be understood 

 only when the general distribution of all these species is taken 

 into account. G. affinis finds in southern Illinois the northern 

 limit of its range, its occurrences beyond that boundary being 

 evidently merely accidental. In its general distribution it goes 

 southeast to Florida and southwest to Mexico, while the three 

 other species are so distributed that Illinois is in the midst of 

 the area occupied by them. These general occupants of our 

 area have come to avoid each other locally in great measure, as 

 shown by their relatively small coefficients of association an 

 adjustment forced upon them by the competitive relations in 

 which they otherwise would live wjhlle G. affinis, entering the 

 territory of these three species only at its southern border, has 

 not become ecologically adjusted to them, and is consequently 

 to be found in their favorite haunts more frequently than they 

 are in those of each other. These various relations may be 

 more clearly shown by the following table. 



TABLE OF ASSOCIATE RELATIONS OF FUNDULUS DISPAR, 

 F. NOTATUS, AND GAMBUSIA AFFINS 



FAMILY AMBLYOPSID^ 



THE BLINDFISHES 



Body moderately elongate, compressed behind; head long and depressed; 

 body with small cycloid scales, irregularly placed, and more or less imbedded, 

 so that the body appears naked; head naked, the surface sometimes crossed 

 by papillary ridges; lateral line wanting; skeleton osseous; anterior vertebrae 

 simple; ventral fins small or wanting, abdominal; no spines in fins; dorsal 

 nearly opposite anal; caudal truncate or rounded; no mesocoracoid; gill- 



23 F 



