204 Bulletin 4J, United States National Museiun. 



aa'. Lower jaw with the lip developed as a fleshy lobe on 



each side ; teeth 4-4 ; dorsal anterior ; scales 



rather small, 40 to GO. Phenacobitjs, 125. 



7j>/. Scales very small, 85 to 90 in lateral line; body long and low, 



subtereto ; mouth small, the upper jaw little protractile ; 



teeth 4-4. Evaura, 120. 



XX. Upper jaw not protractile; lips fleshy; body elongate, covered 



with minute scales; teeth small, 1,4-4,1. 'XiAnOciA, 127. 



low. Maxillary with a small barbel at or near its extremity. 



d'. Prema.\illarics nut protractile ; the frenum very broad ; teeth 2, 

 4-4, 2; scales small, dorsal posterior. RiiiNicnTiivs, 128. 



dd'. Premaxillaries protractile (rarely joined to the forehead by a 

 narrow frennni). 

 e'. Scales very small, (10 to 90 in lateral line ; lateral line often 

 incomplete ; dorsal posterior. Agosia, 129. 



ee'. Scales lai'ge, 35 to 55 ; dorsal median ; lateral line complete. 

 /'. Teeth 4-4, or 1, 4-4, 1 or 0, the lesser row with never 

 more than 1. Hybopsis, 1.30. 



ff'. Teeth usually 2, 4-4, 2, the lesser row rarely with less 

 than 2. 

 g'. Head convex above ; teeth without grinding surface ; 

 barbel not quite terminal. Couesius, 131. 



gg'. Head more or less flattened above ; teeth with grind- 

 ing surface ; barbel terminal. Plattgobio, 132. 

 EXOGLOSSINS! : 



mm. Lower jaw singularly formed, the dentary bones parallel, united for their 

 whole length. 

 /('. Premaxillaries not protractile; mandible with a conspicuous fleshy lobe on 

 each side at the base; teeth 1, 4-4, or 1 ; no barl>el; scales moderate. 



exoglo.ssum, 133. 

 Plagopterin.*; : 



AA. Dorsal fin short, posterior, with a strong spine, composed of 2, the posterior received into 

 a longitudinal groove of the anterior; inner border of the ventral fins adherent to the 

 body; teeth hooked, without grinding surface, in 2 rows. 

 %'. Body with small scales; teeth 2, 4-4, 2; no barbels. Lepidomeua, 134. 



W. Body scaleless; teeth 2, 4-5, 2. 



j'. Maxillary without barbel. Meua, 135. 



jj'. Maxillary with a barbel. Plaoopterus, 13G. 



100. CAMPOSTOMA, Agassiz. 

 (Stone Rollers.) 



Oampostoma, AoASSiz, Amer. .Tourn. Sci. Arts, 1855, 218, (auoninhnn). 



Body moderately elongate, little compressed. Mouth normal, the jaws 

 with thick lips and rudiment of a hard sheath. Premaxillaries protractile; 

 no barbel. Teeth 4-4, or 1, 4-4, 0, with oblique grinding surface, and a 

 slight hook on 1 or 2 teeth. Air bladder suspended in the abdominal 

 cavity, and entirely surrounded by many convolutions of the long alimen- 

 tary canal, which is 6 to 9 times the total length of the body; ovaries 

 similarly inclosed by the alimentary canal. Peritoneum black. Psendo- 

 branchito present. Scales moderate. Lateral line present. Dorsal nearly 

 over veutrals. Anal short. No spines. Herbivorous. Sexual difterences 

 very great, the males being covered with large tubercles in spring. The 

 singular arrangement of the intestines in relation to the air bladder is 

 peculiar to Campostoma among all known fishes. Size moderate. {Ka/u-^'i/, 

 curve; aro/ia, mouth) 



