AMBLYOPSIDy€ — -THE BLINDFISHES 



217 



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 occur- 

 rences 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 Illi- 

 nois 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 associa- 

 tion — an adjustment forced upon them by the competitive relations 

 in which they otherwise would live — while 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 mote clearly 

 shown by the following table. 



Table of Associate Relations of Fundulus dispar, 



F. NOTATUS, AND GaMBUSIA AFFINIS 



Species 



F. dispar. . 



F. notatus. 



F. dispar. 



G. affinis. 



Collections 



83 

 210 



83 

 18 



Joint occur- 

 rences 



Frequency 

 coefficients 



F. notatus. 



G. affinis. . 



210 

 18 



11 



4.37 



Family AMBLYOPSID^ 



(the blindfishes) 



Body moderately elongate, compressed behind; head long and de- 

 pressed; 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 vertebra; simple; ventral fins small or wanting, abdom- 

 inal; no spines in fins; dorsal nearly opposite anal; caudal truncate or 



