Jordan and Evermann. — Fishes of North America. 207 



related to the European genus, Chondrostoma, dififering chiefly in the 

 absence of pseudobianchiiu and of the horny mandibular plate. {opOu^, 

 straight; u6oix, tooth.) 



»30. OKTHODON MIC'KOLKPIDOTUS (Ayres). 

 (Black-fish.) 

 Head 4; depth 4i. D.9; A. 8; scales 21-105-12; Vert. 24+20. Teeth 

 6-6 or 6-5, very long. Body elongate, not much compressed. Head mod- 

 erate, flattish above, with two bony ridges ; snout very broad ; eye small, 

 about half length of snout. Mouth terminal, somewhat oblique, broad, 

 the maxillary not extending to the eye. Fins rather large ; the caudal 

 strong. Lateral line decurved. Coloration plain olivaceous, paler below. 

 Size large. Length 12 to 16 inches. Lower Sacramento and San Joaquin 

 rivers and neighboring streams; locally abundant in quiet waters. 

 (fiiKpo?i£wi()oTug, small-scaled. ) 

 Gila microlepiiliihi, Ayres, Proc. Cal. Ac. Nat. Sci., I, 21, 1855, Sacramento and San Joaquin 



rivers, California. (Coll. W. 0. Ayres.) 

 OrthodoH mirr(jtf]udo(,is, GlUARD, Pac. K. R. Surv., Fish., 237, pi, Liti, fig. 1-4, 1858; GiJNTHBB, 



Cat., VII, 275, 1868; Jordan & Gilbert, Synopsis, 152, 1883. 



102. OXYGENEUM, Forbes. 



Oxijgeneum, Forbes, Bull. 111. Lab. Nat. Hist., 1855, 136, (pnlverulentitm). 



Body elongate, subterete; head small, conical ; mouth large, terminal; 

 upper jaw protractile, with fleshy lips; lower jaw thin, with sharp, hard 

 edge; no pseudobranchiie; scales rather small; lateral line complete. 

 Alimentary canal elongate, more than twice length of body ; teeth 4-5 or 

 5-5, in one row, not strongly hooked; peritoneum black. Herbivorous 

 species of small size, (ofif, sharp; y'evvg, chin.) 



331. OXYGENEUM PULVERULEXTUM, Forbes. 



Head 4^; depth 5; eye 4. D. 8; A. 7. Lateral line 63; 31 scales before 

 the dorsal. Form of Moxosioma ; head small, conical ; mouth large, 

 terminal; gill rakers slender. Breast scaly. Dorsal fin high. Color 

 pale, the back and sides dusted with dark specks. Length 2i inches. 

 Illinois River. (Forbes.) {imlverulentus, dusted.) 



Oxygeneuin puloerulenlum, Forbes, Bull. 111. Lab. Nat. Hist., 1885, 136, Illinois River. (Coll. 

 Forbes.) Jordan, Man. Vertebrates, Ed. v, 52, 1890. 



103. ACROCHEILUS, Agassiz. 

 (Chisel-mouths.) 



Acrocheilus, AoASSiz, Amer. Journ. Sci. Arts, 1855, 211, (alutaceus). 



Body elongate, little compressed. Each jaw with a large, straight, 

 horny plate, sharp externally and very conspicuous. Upper jaw pro- 

 tractile ; no barbel. Teeth 4-5, stout, hooked, with broad masticatory 

 surface. Intestinal canal elongate; peritoneum black. Pseudobranchias 

 present. Scales small, loosely imbricated. Lateral line present. Dorsal 

 fin slightly behind ventrals. Anal basis moderate. Caudal fin broad, its 

 rudimentary rays recurrent on the caudal peduncle. Size rather large. 

 A single species, American. (uKpoc, sharp ; ;i;«Aof, lip.) 



