HIODON — MOONEYES 43 



articulated to end of premaxillary and forming lateral margin of upper jaw; 

 sid3s 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 Sueuk 



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 11 or 12 developed rays, 

 inserted in front of ventrals; eye greater than interorbital space. .. .tergisus. 



HIODON ALOSOIDES (Eafinesque) 

 northern mooneye 



Raflnesque, 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 species: mouth large, maxillary reach- Fig. 11 



ing 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 1^ in head; pectorals longer than in the next species, 

 1.1 to 1.2 in head. Scales 6, 56-58, 7 or 8; lateral Une complete. 



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

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



