66 The Food of the Smaller Fresh- Water Fishes. 



under the genus and sometimes under the special group to which 

 the genus is assigned. 



FAMILY APHREDODERID^. 



This family is represented by a single peculiar species [Aphre- 

 doderus sat/anus), resembling the sun-fishes in most of its char- 

 acters, but remarkably distinguished by tlie fact that the vent, 

 although occupying the normal position in the young, opens in 

 the adult far forward under the head, moving gradually to the 

 front with increasing size. This fish is not over three inches in 

 length. It occurs in rivers and smaller streams, as well as in lakes 

 and ponds throughout the State. We have collected it from the 

 Illinois River and various tributaries, as well as from the lakes 

 connected with that stream, and from ponds and creeks through- 

 out Southern Illinois. It has also been taken in the Calumet 

 River near Chicago, and from lakes in that vicinity, but is not 

 known to occur in Lake Michigan. It is said to be nocturnal in 

 its habits, by Dr. C. C. Abbott, who kept specimens in an aqua- 

 rium for some time.* The same author reports that in confine- 

 ment it feeds voraciously upon small fishes, especially immature 

 Cyprinid.ie ; and for this reason he bestowed upon it the name of 

 pirate perch, by which it has become generally known among 

 ichthyologists. The observations presently to be detailed will 

 show, however, that his specimens were doubtless forced to feed 

 so largely upon fishes for want of food more natural to them," 

 since in their native haunts fishes make but a small percentage of 

 their ordinary food. 



The intestine of this species is short and simple, less than the 

 length of the head and body without the tail, and distinguished 

 only by the character previously mentioned. The gill apparatus 

 is ineffective, the rakers being very short, thick, blunt, and few, 

 and covered with short spirniles. The pharyngeal jaws consist 

 of small plates, covered with short, sharp spinulose teeth, similar 

 to those of the sun-fishes. The mouth is large, but not remarka- 

 bly protractile. 



The specimens dissected number nineteen, representing seven 

 different dates and localities, throughout Central and Southern 

 Illinois. Some were taken from small temporary ponds left by 



»Proc. Phil. Acad. Nat. Sci., 1861, p. 95. 



