HY0D0NTIDJ3. 375 



Fam. 19. HYODONTIDiE. 



Body covered with cycloid scales ; head naked ; 

 barbels none. Margin of the upper jaw formed by 

 the intermaxillaries mesially, and by the niaxillaries 

 laterally, the latter being articulated to the end of 

 the former. Opercular apparatus complete. Adipose 

 fin none ; the dorsal fin belongs to the caudal portion 

 of the vertebral column. Stomach horseshoe-shaped, 

 without blind sac; mtestine short; one pyloric ap- 

 pendage. Pseudobranchite none ; air-bladder simple *, 

 Gill-openings wide. The ova fall into the abdominal 

 cavity before exclusion. 



Fresh waters of North America. 

 Only one genus is known. 



1. HYODON. 



Hiodon, Lesxcur, Juurn. Ac. Nat. Sc. Philad. i. p. 304, 

 Glossodon, Meckel, in Russegger^s Heisen, i. p. 1033. 



Body oblong, compressed, with a part of the abdomen trenchant ; 

 cleft of the mouth of moderate width, oblique, upper jaw overlap- 

 ping the lower. Bauds of small teeth in the jaws, on the palatine 

 and pterygoid bones, along the vomer, sphenoid, and hyoid ; tongue 

 with an outer series of larger teeth. Dorsal fin short, opposite to 

 the anterior part of the anal, which is long ; caudal forked. Pectoral 

 and ventral fins well developed. Gill-membranes entirely separate, 

 terminating in front below a transverse fold across the middle of 

 the throat. Branchiostegals in moderate number. 



Presh waters of North America. 



1. Hyodon tergisus. 



The Moon-eye. 



Hiodon tergisus, Lesucur, I.e. p. 366; Kirtland, Rep. Zool. Ohio, 



pp. 170, 1135; and Bout. Journ. Knt. Hist. v. 1846, p. 338; Dekay, 



New York Faun. Fish. p. 265, pi. 41. fig. 130; Cur. ^- Val. xL\. 



p. 309, pi. 572 ; Girard, U. S. ^- Pac. R. R. Krped. Fish. p. 332, 



pi. 75. figs. 1-4 (not 4-7). 



* Lesueur describes two additional .small subglobular air-vessels at the ante- 

 rior end of tlie air-bladder, proliably mi.staking portions of tlie comenhat (bicker 

 outer iiienibriiiH' of tlie air-bladder as separate divisions. 



