190 
U. S P. R. R. EXP. AND SURVEYS—ZOOLOGY—GENERAL REPORT. 
purple. The dorsal, caudal, and pectorals are dark greyish olive; the rays of the anal and 
ventrals are olive, whilst their interdigital membrane is purple. 
A specimen, fourteen inches in total length, was caught in Tomales Bay, California, by E. 
Samuels. 
Plate XL, fig. 1, represents Rhacochilus toxotes, somewhat reduced in size. 
Eig. 2 is a scale from the dorsal region. 
Eig. 3, a scale from the lateral line. 
Fig. 4, a scale from the abdominal region. 
List of specimens. 
Catal. 
No. 
No. of 
spec. 
Sex and 
age. 
Locality. 
When col¬ 
lected. 
Whence obtained. 
Nature of 
specimens. 
Collected by— 
539 
i 
Adult.. 
Tomales Bay, Cal- 
1855 
Mr. E. Samuels_ 
Alcoholic. 
Mr. Samuels._ 
HYSTEROCARPUS, Gibbons. 
Gen. Char. —Head is small or of medium size. Mouth small, gape slightly oblique ; jaws sub-equal. Lips rather thin ; lower 
one free all round. Premaxillaries quite protractile. Teeth sub-conical, occupying the fore part of the jaws only, and disposed 
upon one single row. Spinous portion of dorsal much longer and somewhat higher upon its middle than the soft portion. 
Anterior articulated rays of anal simple, and preceded by three small spines. Cauda] fin furcated. Branchiostegals, five on 
either side. Scales large. Lateral line concurrent with the dorsal outline. No scales upon the fins. Dorsal groove running 
nearly along the entire base of the fin ; sheath formed of one row of scales only. 
Syn.— Hysterocarpus , Gibbons, in Proc. Acad. Nat. Sc. Philad. VII, 1854, 124. 
This genus bears a general resemblance to Abeona, Ennichthys, and Holconotus, by the outline 
of its dorsal fin, the spinous portion of whicli is higher upon its middle than the highest articu¬ 
lated rays. It differs, however, from them by that same spinous portion of the fin being much 
more extended than the soft, which constitutes only a fraction of the entire base or length. 
From Ennichthys and Holconotus it furthermore differs by the presence of one single row of teeth 
upon the jaws, instead of two. The base of the anal fin is also shorter. The anterior articu¬ 
lated rays of the anal are simple, whilst they dichotomise in Abeona, Ennichthys, and Holconotus. 
Its affinities with Abeona are apparently closer, since there is but one series of maxillary teeth ; 
still the lower lip is free all round as is the case in Ennichthys and Holconotus, whilst it is 
attached by a frenum to the symphysis of the jaw, as in Abeona. From the latter it may yet 
be distinguished by a shorter caudal peduncle. 
HYSTEROCARPUS TRASKII, Gibbons. 
Plate XXYI, Fig. 14. 
Spec. Char._ Body sub-elliptical in its profile ; nape convex, frontal line depressed. Eye circular, of medium size. Posterior 
extremity of maxillary extending to a vertical line drawn in advance of the anterior rim of the orbit. In the male the upper 
regions are dark or purplish brown, unicolor ; yellowish olive, spotted with black, on the lower portion of the sides ; throat and 
belly yellowish golden. In the female the back is ash-colored, with irregular black patches, approximating somewhat to inter¬ 
rupted bands, across the sides ; belly lemon yellow. 
Stn .—Hysterocarpus traskii, Gibbons, in Proc. Acad. Nat. Sc. Philad. VII, 1854, 105 & 124.— Grd. in Proc. Acad. Nat. 
Sc. Philad. VIII, 1856, 136. 
