FISHES—CYPRINIDAE-SIBOMA ATRARIA. 
297 
distant between the insertion of the pectorals and the tip of the middle rays of the caudal. The 
origin of the ventrals is situated nearly opposite the anterior margin of the dorsal, else somewhat 
posterior to it; they are posteriorly rounded or sub-convex, quite broad when expanded, their 
tips overlapping the vent and reaching the anterior margin of the anal fin when extended in 
that direction. The pectorals are of moderate development, posteriorly rounded, sub-ovate in 
their outlines, and far from extending to the origin of the ventrals. 
D 2, 8 + 1; A 2, 8 + 1 ; C 7, 1, 9, 8, 1, 8 ; Y 1, 9 ; P 17 or 18. 
The scales are large, deeper than long, anteriorly sub-truncated, posteriorly rounded, with 
radiating furrows upon the posterior section alone. The lateral line is slightly deflexed upon 
the thoracic region, whence it becomes nearly straight to the base of the caudal, being nearly 
equidistant between the base of the dorsal fin and the insertion of the ventrals. 
The dorsal region is light purplish brown, the middle of the scales exhibiting more of the 
brown than of the purple tint. The flanks appear sometimes as though obsoletely clouded, 
whilst the abdominal region is of a uniform dull yellowish tint. The fins are unicolor; the dorsal 
and caudal greyish, the others yellowish. 
References to the figures —Plate LXIY, fig. 1, represents Siboma crassicauda, size of life ; fig. 
2 is a dorsal scale ; fig. 3, a scale from the lateral line ; fig. 4, a scale from the abdominal 
region. 
List of specimens. 
Catal. 
No. 
Cor’g No. 
of teeth. 
No. of 
spec. 
Age. 
Locality. 
When 
collected. 
Whence obtained. 
Nature of 
specimen. 
Collected by— 
235 
2772 
2 
Adult. 
Rio San Joaquin, Cal. 
1853 
Lt. R. S. Williamson. 
Alcoholic. 
Dr. A. L. Heermann. 
2. SIBOMA ATRARIA, Grd. 
Spec. Char. —Body somewhat elongated, sub-fusiform in profile. Peduncle of the tail rather stout; head constituting a 
little less than the fourth of the total length ; its profile gently sloping forwards, the snout being sub-conical. Mouth small; 
posterior extremity of the maxillary extending to a vertical line drawn immediately behind the nostrils. Eye small and sub- 
circular ; its diameter entering five times and a half in the length of the side of the head. Anterior margin of dorsal fin nearer 
the insertion of the caudal than the extremity of the snout. Blackish or brownish black above ; greyish white beneath. 
Syn .—Siboma atraria, Grd. in Proc. Acad. Nat. Sc. Philad. VIII, 1856, 208. 
The largest specimen of this species which we have examined is about seven inches in length, 
and although small, compared to the specimens of S. crassicauda , to which we had to compare 
it, yet the distinctive features between the two species appear very striking. And first of all, 
the imbrication of the scales in S. atraria is such as to expose more of their surface than in S. 
crassicauda , and, moreover, the lateral line in S. atraria runs along the seventh row of scales 
from the insertion of the ventrals upwards, leaving eleven rows above it, to the base of the 
dorsal fin, whilst in 8. crassicauda there are as many rows of scales below as above the lateral 
line. The absolute number of longitudinal rows of scales is the same in both species. The 
head is proportionally larger than in S. crassicauda, but the fins are much less developed. The 
dorsal is a good deal larger than the anal, although both fins are similar in shape ; their upper 
edge being sub-concave. The anterior margin of the anal is nearer the tip of the inferior lobe 
38 a 
