FISHES OF STREAMS TRIBUTARY TO MONTEREY BAY. 
63 
HESPEROLEUCUS, new genus. 
The generic name Hesperoleucus is here used for a small group of closely related cyprinoid fishes 
previously included with others in the genus Rutilus or Myloleucus. The species of Hesperoleucus 
have the insertion of the dorsal fin posterior to the ventrals, by which character they may be distin- 
guished from Myloleucus. They also have a shorter head, more slender body, and a more nearly 
horizontal lower jaw. The pharyngeal teeth number 4-5, 4 on the right side, with a narrow but well- 
developed grinding surface. Hesperoleucus symmetricus may stand as the type of the genus. < 
Hesperoleucus is a genus peculiar to the Sacramento River fauna. Its species inhabit the smaller 
tributaries of the rivers that flow into the Sacramento and San Joaquin, some of the coastal streams 
north of the Golden Gate, the creeks tributary to San Francisco Bay, and the rivers flowing into 
Monterey Bay. They have been included in the species Rutilus symmetricus by recent authors, as 
were also several forms belonging to the genus Myloleucus. The latter is an assemblage of comparatively 
large lake and channel fishes which do not usually frequent the smaller creeks, but live mainly in the 
deep, sluggish pools of the rivers. They occur abundantly in certain lakes of the Great Basin, where 
they grow to a large size. 
In a previous paper ® the writer referred to three well-defined geographic races of Hesperoleucus 
(Rutilus) thus; "A minnow of this type occurs in the Navarro, Gualala, Russian, and Napa Rivers. 
Specimens from the Russian and Napa Rivers are alike in all respects, and they in turn agree closely 
with representatives from the streams tributary to San Francisco Bay. In a majority of cases the dorsal 
fin has 9 rays and the anal 8. The snout is rather pointed, the caudal peduncle slender, and the fins 
long, the whole body being trim and well proportioned. Examples from the Navarro and Gualala 
Rivers are distinguished from these by having generally 8 rays in the dorsal fin, a more robust body, 
with a deeper caudal peduncle, and a more rounded and shortened snout. The fins are also shorter 
and somewhat less acute. While examples from the Navarro and Gualala Rivers thus agree in differing 
from specimens taken in the neighboring basins, individuals from each of these streams bear a dis- 
tinctive local stamp by which they may be recognized without difficulty, the Navarro exampleshaving 
mostly one more ray in the anal fin, and larger scales in the series above the lateral line. It has been 
shown that individuals from the partly isolated rivers tributary to San Francisco Bay are alike in all 
points, and that these are scarcely to be distinguished in any particular from individuals from the Napa 
and Russian Rivers. Hence it appears that there are three well-differentiated forms of Rutilus in this 
somewhat restricted region, each of which occupies a distinct hydrographic basin or series of contiguous 
basins. When, however, the field is broadened and specimens from distant parts of the Sacramento 
and San Joaquin Basins are brought togetlier, similar variations of a local nature are found to occur, but 
whether any geographical significance may be attached to these can not be known until more extensive 
observations have been made.” Since then more material has been secured, including specimens of 
H. symmetricus from the type locality, and many examples of a well-differentiated form from the streams 
tributary to Monterey Bay. In order to deal intelligently with the latter it now seems best to restrict 
the name symmetricus to fishes of the genus inhabiting the rivers of the San Joaquin Valley, to recognize 
the form frequenting the streams in the immediate region of San Francisco Bay, and likewise that of 
the Navarro River, Gualala River, and of the streams tributary to Goose Lake, descriptions of which 
follow in the order indicated. 
Hesperoleucus symmetricus (Baird and Girard)® is not to be confused with Alganseaformosa Girard, 
Algansea obesa Girard, A'lyloleucus pulverulentus Cope, nor Myloleucus parovanus Cope. This species, 
“ Snyder, J. O.: The fishes of the coastal streams of Oregon and northern California. Bulletin Bureau Fisheries, vol. xxvu, 
1907, p. 175. 
^ Jordan and Evermann: Fishes North and Middle America, Bulletin 47, TJ. S. National Museum, p. 246, synonymy of 
Rutilus symmetricus. Through the kindness of the National Museum authorities the writer has been permitted to examine the 
types of Pogonichthys symmetricus Baird and Girard, and also of Algansea formosa Girard. The latter, which is from Merced 
River, and in a bad state of preservation, appears to be indistinguishable from Myloleucus thalassinus of the upper Pit River and 
Goose Bake. It is a Myloleucus, not a Hesperoleucus, and if when better specimens from the Merced are examined no differen- 
tiating characters appear, M. formosa will stand in place of M. thalassinus, its known range extending from the lower San Joaquin, 
to the northern tributaries of Goose Lake. 
