FISHES—CYPKINIDAE—ACOMUS GENEROSUS, 
221 
The origin of the ventrals is situated in advance of the middle of the dorsal. The tips of the 
pectorals reach a vertical line drawn from the origin of the dorsal. 
D 15 ; A 10 ; C 4, 1, 8, 8, 1, 3 ; V 10 ; P 17. 
There are two rudimentary rays at the anterior margin of both the dorsal and the anal, and 
one at the exterior margin of the ventrals ; these are all summed up in the formula. Thirteen 
rows of scales may be counted between the origin of the ventrals and the anterior margin of the 
dorsal; the scales themselves are longer than deep, provided with radiating furrows upon their 
anterior and posterior sections, the margin of which is irregularly convex. The lateral line 
runs through the median row of scales. 
References to the figures .—Plate XLIX, fig. 1, represents, size of life, Ptychostomus hay deni, 
from the Yellowstone river. Fig. 2, a scale from the dorsal region. Fig. 3, a scale from the 
lateral line. Fig. 4, a scale from the abdominal region. 
List of specimens. 
Catal. 
No. 
Corresponding 
No. of teeth 
No. of 
spec. 
Age. 
Locality. 
When 
collected. 
Whence obtained. 
Nature of 
specimen. 
Collected by— 
172 
2759 
2 
Adult. 
Yellowstone river. 
1854 
Col. A. Vaughan . 
Alcoholic. 
Dr. F. V. Hayden 
173 
1 
..do.. 
Missouri river at Fort Pierre 
1854 
Gov. 1.1. Stevens . 
....do.•.. 
Dr. John Evans. 
ACOMUS, Girard. 
Gen. Char. —The head is very elongated; the lips beiDg papillated and the lower one very deeply cleft. The dorsal fin is higher 
than long, and the scales are much smaller upon the anterior region of the body than posteriorly. The pharyugeals are 
gently arched and not expanded; the teeth, compressed and bituberculated, the inner projection conspicuous; the outer one 
obsolete though existing. 
Syn. — Acomus, Gkd. in Proc. Acad. Nat. Sc. Philad. VIII, 1856, 173. 
The lips being papillated and the inferior one cleft as in Catostomus, the distinction between 
this genus and the one just alluded to consists chiefly in a more elongated head and the dispro¬ 
portion in the size of the scales of the anterior and posterior region of the body. The 
pharyngeal hones and teeth will also afford some structural peculiarities, enabling us to 
discriminate between the species belonging to either of these two genera. 
1. ACOMUS GENEROSUS, Grd. 
Spec. Char. —Head constituting the fifth of the total length; mouth moderate sized; lips rather small, covered with uniform 
granules. Eye small, sub-circular; its diameter entering five times in the length of the side of the head. Anterior margin of 
dorsal fin equi-distant between the extremity of the snout and the insertion of the caudal. Extremities of ventrals not reaching 
the vent; their origin taking place under the posterior third of the dorsal. Olivaceous above, blotched with blackish; yellowish 
olive beneath. Fins unicolor. 
Syn. —Catostomus ( Acomus) generosus, Grd. in Proc. Acad. Nat. Sc. Philad. VIII, 1856, 174. 
It is a rather short and contracted species, particularly when compared to A. griseus. The 
head constitutes about the fifth of the total length. The lips are less developed than in A. 
griseus, and the tubercles uniform throughout. The eye is moderate sized and sub-circular ; its 
diameter entering five times in the length of the side of the head. The anterior margin of the 
dorsal fin is equi-distant between the tip of the snout and the insertion of the caudal fin. The 
