58G CONTRIBUTIONS TO NORTH AMERICAN ICHTHYOLOGY IV. 



nature by Dr. Gibbous and Professor Agassiz, in 1853, these fishes have 

 been the subject of much interest to anatomists. 



Fishes of the Pacific coast of North America, inhabiting bays and 

 the surf on sandy beaches. One species {Hysterocarpus traski) inhabits 

 fresh waters, one {'■'■Ditrema''^ molaceum) is found in Australia, and 

 another {Ditrema temmincM) is found in Japau. The species reach a 

 length of from G to 18 inches, and are very abundant where found. 

 They are much used for food, but the flesh is poor and tasteless. Most 

 of them fet'd on Crustacea, but one genus {Aheona) is j)artly or wholly 

 herbivorous. Geuera 8; species 20. 



(Emhiotocidw GilutberJ iv, 244-r231.) 



"Spinous dorsal longer than tlie soft part, of 16-18 spines; second anal spine the 

 largest. ( Il'jsterocarpince. ) 

 a. Scales large ; teeth moderate, conical, in one series ; lower lip without frenum. 



Hystkrocarpus, 307. 

 ** Spinous dorsal shorter than the soft x^art, of S-11 spines; anal spines graduated. 

 (E^nbiotocir.a.) 

 h. Scales large (40-50 in the lateral line); soft dorsal and anal more or less short- 

 ened. 

 c. Teeth incisor-like, most of thorn obtusely thrce-lobed ; lower lip with a nar- 

 row freuuui Abeona, 308. 



cc. Teeth conic, entire Micrometrus, 309. 



ib. Scales small (60-75 in the lateral line). 



d. Teeth in two series in each jaw Amphistichus, 310. 



dd. Teeth in a single series in each jaw. 



e. Lower pharyngeal bone normal (with the posterior margin concave, the 

 the lateral horns well developed, and the teeth all on the same plane, 

 some conical, some truncate). 

 /. Lower lip with a frenum, its edge entire. 



g. Abdomen much longer than the base of the short anal fin. 



Hypsurus, 311. 

 gg. Abdomen much shorter than the base of the long anal fin. 



Ditrema, 312. 

 ff. Lower lip without frenum, its free fold incised behind ; lips very 



large Rhacochilus, 313. 



ee. Lower pharyngeals peculiar, very large, posteriorly convex, the lateral 

 horns little developed, the teeth on two separate planes which meet 

 at an angle, the anterior teeth hexagonal and tessellated, the posterior 

 appressed forwards Damalicuthys, 314. 



307.— HYSTEROCARPUS Gibbons. 



(Gibbons, Daily Placer Times and Transcript, May 18, 1854, and in Proc. Acad. Nat. 

 Sci. Phila. 1854, 124: type Hysterocarpus traslci Gibbons.) 



Body ovate, the back strongly elevated and convex ; head small, the 

 snout projecting; mouth small, with one series of rather large, bluntly 

 conical teeth; the jaws about equal; lips not much enlarged, the lower 

 forming a free border, without frenum ; gill-rakers moderate, widely set; 

 branchiostegals 5; scales rather large, silvery; spinous dorsal very 



