FISHES—CYPRIN1DAE— C ATOSTOMUS. 
223 
3. ACOMUS LACTARIUS, Grd. 
Plate L. 
Spec. Chau. —Head constituting somewhat less than the fifth of the total length. Mouth small; lips well developed, covered 
with uniform granules. Eye large, sub-circular; its diameter entering five times in the length of the side of the head. Anterior 
margin of dorsal fin somewhat nearer the insertion of the caudal than the extremity of the snout. Insertion of ventrals situated 
opposite the posterior half of the dorsal; their tip extending to the vent. Greyish brown above; greyish white beneath. 
Syn. — Catostomus ( Acomus) lactarius, Grd. in Proc. Acad. Nat. Sc. Philad. VIII, 1856, 174. 
it is closely allied to the preceding species, from which it differs by a stouter head, larger 
eyes, and larger scales on the body. The scales are longer than deep, sub-quadrangularly 
elliptical, with radiating furrows upon their anterior and posterior sections alone ; a trait of 
structure by which they may readily he distinguished from those of the preceding species. The 
upper margin of the dorsal fin is concave, whilst it is nearly straight in A. griseus. 
D 13 ; A 10 ; C 4, 1, 8, 8, 1, 5 ; V 11 ; P 17. 
The color is greyish brown above, and greyish white beneath. The fins being greyish olive. 
References to the figures. —Plate L, fig. 1, represents Acomus lactarius, size of life. Fig. 2, a 
scale from the dorsal region. Fig. 3, a scale from the lateral line. Fig. 4, a scale from the 
abdominal region. Fig. 5, the young of the same species. 
List of specimens. 
Catal. 
No. 
Cor. No. 
of teeth. 
No. of 
spec. 
Age. 
Locality. 
When col¬ 
lected. 
Whence obtained. 
Nature of 
specimen. 
Collected by— 
257 
2804 
2 
Adult. 
Milk river, affluent of 
1853 
Gov. 1.1. Stevens. 
Alcoholic.. 
Dr. Geo. Suckley... 
Upper Missouri. 
258 
5 
Young. 
CATOSTOMUS, Lesu. 
Gen. Char. —Head moderately elongated. Lips papillated; lower one deeply cleft. The dorsal fin is generally longer than 
high, and the size of the scales nearly equal anteriorly and posteriorly. The pharyngeals are provided with a little expansion 
inferiorly; the teeth being compressed, with the inner projection of the crown alono developed. 
Syn.— Catostomus, Lesu. in Jour. Acad. Nat. Sc. Philad. 1,1817, 89.— Rafin. Ichth. Ohiens. 1820, 53.—Cuv. Rbgn. Anim. 
2d ed. 11,1829; &, ed. illustr. Poiss. 220.— Storer, Rep. Fish. Mass. 1839,83; Synops. 1846, 166; &, 
Hist. Fish Mass, in Mem. Amer. Acad. New S. V, 1855, 290.— DeKay, N. Y. Faun. IV, 1842, 196.— Heck. 
in Russeg. Reisen, I, ii, 1842,1022.—Cuv. & Val. Hist. nat. Pois. XVII, 1844,418.— Agass. Lake Sup. 1850, 
356; &, in Amer. Journ. Sc. 2d ser. XIX, 1855, 92.— Grd. in Proc. Acad. Nat. Sc. Philad. VIII, 1856, 174. 
As characterized above, this genus contains yet numerous species, and, what is very curious, 
it includes several species from the western slope of the Rocky mountains, together with those 
originally known in the eastern States. 
