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 trasl'i) inhabits 
fresh waters, one {^^Ditrema^’ violaeeum) is found in Australia, and 
another (Ditrema temminchi) is found in Japan. The species reach a 
length of from 0 to 18 inches, and are very abundant where found. 
They are much used for food, but the fiesh is ]»oor and tasteless. Most 
of them fee<l on Crustacea, but one genus (Aheona) is partly or wholly 
herbivorous. Genera 8; species 20. 
{Emhiotodda Gilutber, iv, 244-:251.) 
'^Spinous dorsal longer than the soft i)art, of 16-18 spines; second anal spine the 
largest. {Ihjsterocarpinh;. ) 
a. Scales large ; teeth moderate, conical, in one series ; lower lip without frenuin. 
Hysterocarpus, 307. 
** Spinous dorsal shorter than tlic soft XJRi’t, of S-11 spines; anal spines graduated. 
(Embiotocinw.) 
b. Scales large (40-50 in the lateral line); soft dorsal and anal more or less short- 
ened. 
c. Teeth incisor-like, most of them obtusely three-lohed ; lower Jip with a nar- 
row frenum Abeona, 308. 
cc. Teeth conic, entire Micrometres, 309. 
hb. Scales small (60-75 in the lateral line). 
d. Teeth in two series in each jaw Amphisticiius, 310. 
dd. Teeth in a single series in each jaw. 
e. Lower pharyngeal hone 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 frenuin, 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, vei’y 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 Damalichthys, 314. 
307.— HVSTEROCARPUS Gibbons. 
(Gibbons, Daily Placer Times and Transcript, May 18, 1854, and in Proc. Acad. Nat. 
Sci. Phila. 1854, 124: type Hgsterocarjms trasJci Gibbons.) 
Body ovate, tbe 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; 
brauchiostegals 5; scales rather large, silvery; spinous dorsal v^ery 
