34 FIELD COLUMBIAN MUSEUM ZOOLOGY, VOL. V. 



dorsal fin low, long, with concave edge; caudal fin broad and strong, 

 with numerous rudimentary rays; pectorals moderate. 



Color plain, olivaceous. Length 2 feet or more. 



A very peculiar Sucker, known only from the basin of the Colorado 

 River. It reaches a weight of 8 to 10 pounds. 



13. Myzostoma Rafinesque. 

 RED-HORSE SUCKERS. 



Moxostoma Rafinesque, Ichth. Ohiensis, 54, 1820. (Type, Catos- 

 tomus anisurus Rafinesque.) 



Body more or less elongate, nearly terete- usually more or less 

 compressed posteriorly; suborbital bones very narrow; fontanelle 

 present; mouth inferior; lips plicate, the lower not deeply incised; 

 jaws without cartilaginous sheath; opercular bones moderately devel- 

 oped, nearly smooth; isthmus broad; gill rakers weak, rather long; 

 pharyngeal bones rather weak; teeth compressed, the lower 5 or 6 

 stronger than the others, which rapidly diminish in size upward, each 

 with a prominent internal cusp. Scales large, nearly equal in size 

 over the body and not especially crowded anywhere; lateral line de- 

 veloped, slightly curved anteriorly, fins all developed; caudal forked; 

 anal fin short and high; air bladder with three chambers. A group of 

 large-scaled suckers chiefly inhabiting the streams of United States 

 east of the Rocky Mountains. 



KEY TO THE SPECIES OF MYZOSTOMA. 



a. Distance from tips of pectorals to base of ven- PAGE 



trals sX m the length of the pectoral fin. congestum 34 



aa. Distance from tips of pectorals to base of ven- 



trals 2^ in length of pectoral austrinum 35 



30. Myzostoma congestum (Baird & Girard). LISA. 



Catostomus congestus Baird & Girard, Proc. Acad. Nat. Sci. Phila., 



1854, 27; Rio Salada, Texas. 

 Ptychostomus albidus Girard, Proc. Acad. Nat. Sci. Phila., 1856, 



172; Rio San Juan, Monterey, Nuevo Leon; near Monterey. 

 Moxostoma congestum Woolman, Bull. U. S. Fish Comm., 1894, 

 56; Rio Grande, El Paso, Texas: Jordan & Evermann, Bull. 

 U. S. Nat. Mus., 1896, 192: Meek, Field Col. Mus. Pub. 65, 

 1902, 76; Santa Rosalia. 



Basin of the Rio Soto la Marina north to the Rio Grande and west 

 to the upper tributaries of the Rio Conchos in Chihuahua. (San 

 Juan; Montemorelos ; Linares; Garza Valdez; Victoria.) 



