HIODON MOONEYES 43 



ing lateral margin of upper jaw; sides of lower jaw fitting within the 

 upper so that the dentaries shut against the palatines; premaxillaries, 

 maxillaries, and dentaries, vomer, palatines, sphenoid, pterygoids, and 

 tongue with small cardiform teeth; stomach horseshoe-shaped, without 

 blind sac; one pyloric caecum; air-bladder large, with open duct; no 

 oviducts, the eggs falling into the abdominal cavity before exclusion. 



Fresh waters of North America ; a single genus known. The 

 species are of little value as food. 



Genus HIODON Le Sueur 



(mooneyes) 



Characters of genus included above. Three species; two found in 

 Illinois. 



Key to the Species of HIODON found in Illinois 



a. Belly in front of ventrals carinated; dorsal with 9 developed rays, inserted 



behind ventrals; eye less than interorbital space alosoides. 



aa. Belly in front of ventrals not carinated; dorsal with 1 1 or 12 developed rays, 



inserted in front of ventrals; eye greater thaji interorbital space 



tergisus. 



HIODON ALOSOIDES (Rafinesque) 

 (northern mooneye) 



Rafinesque. 1819, J. Phys., 421 (Amphiodon alveoides, misprint). 



J. &G., 259 (Hyodon); M. V., 69; J. & E., I, 413; F., 74 (Hyodon) ; L., 20. 



Length 12 inches; body greatly compressed, 

 greatest width often 3 in adults; depth in length 

 3.3 to 3.7; depth caudal peduncle 1.1 to 1.4 in its 

 length. Color bluish above; sides and belly silvery 

 with more or less golden luster forward' and bluish 

 to pinkish farther back. Head 4.5 to 4.9; width 

 head 1.9 to 2.1 in its length; interorbital space 

 3.6 to 4 in head; eye 3.6 to 4; nose 4.9 to .5.9, 

 more noticeably upturned than in the next §pe- Fig. 11 



cies; mouth large, maxillary reaching past middle 



of orbit, 1.9 to 2.1 in head. Dorsal fin with 9 developed rays, inserted 

 behind' front of anal; anal rays 31; ventrals very short, about If in 

 head; pectorals longer than in the next species, 1.1 to 1.2 in head. 

 Scales 6, 56-58, 7 or 8; lateral line complete. 



This rather large and handsome silver-coated fish is now too 

 rare in Illinois to have any especial significance in our waters. 

 Some years ago it was much more abundant than now in the Mis- 



