20 PROCEEDINGS OF THE ACADEMY OF [1893. 



The caudal fin is emarginate. The general form is moderately 

 slender, much as in our chubs of the genus Semotilus. The length 

 of the head measured above, enters the length to the caudal notch 

 about five times; and when measured on the side about four times; 

 and the depth at the front of the dorsal fin enters the same about 

 four times. The mouth is directed obliquely upward, and its rictus 

 appears to be nearly in the line of the anterior border of the orbit. 

 The paired fins are rather short, the pectorals not reaching the ven- 

 trals, nor the ventrals the anal (No. 8,404). The borders of the 

 dorsal and anal are straight (8,402, 8,404). The ribs and vertebral 

 spines are slender. The vertebral bodies have on each side a lon- 

 gitudinal median keel, which is bounded above and below by a 

 fossa. 



Dimensions. 



mm. 



Length of superior surface of head of No. 8,402 15*5 



Length of No. 8,404a to notch of caudal fin 39'5 



Length of head of No. 8,404a on side 9 



Total length of No. 8,397 160 



Length of head of No. 8,397 on side 41 



Length from end of muzzle to origin of dorsal fin (No. 8,397) 77 



The earliest Cyprinidce in North America whose horizon is posi- 

 tively known are from the Idaho beds of Idaho and eastern Oregon, 

 which are of Pliocene age. It is likely that the lake deposit in 

 which the Aphelichthys lindahlii is found is not of an earlier age 

 than the Idaho beds. Species of existing genera of the family 

 occur, however, in the middle Miocene of Europe. I dedicate the 

 species to my friend Dr. Josua Lindahl, State Geologist of Illinois. 



