FIS HES—EM BIOTOCOIDAE—AMPHISTICHUS SIMILIS. 
203 
The species inhabits the Bay of San Francisco, California. 
Plate XXXIX, fig. 1, represents the male sex of Amphistichus argenteus, somewhat reduced 
m size. 
Fig. 2 is a transverse section across the line of greatest depth of the body. 
Fig. 3 is a scale from the dorsal region. 
Fig. 4, a scale from the lateral line. 
Fig. 5, a scale from the side of the abdomen. 
List of specimens. 
Catal. 
No. 
No. of 
spec. 
Locality. 
When col¬ 
lected. 
Whence obtained. 
Nature of 
specimens. 
Collected by— 
557 
i 
1853 
558 
i 
1853 
Lt. A. W. Whipple. 
559 
i 
1853 
Lt. W. P. Trowbridge.. 
2. AMPHISTICHUS SIMILIS, Grd. 
Plate XXXVI, Figs. 5-9. 
Spec. Char. —General form regularly sub-elliptical. Snout sub-conical. Posterior extremity of maxillary reaching a 
vertical line passing in advance of the pupil. Spinous portion of dorsal as high as the soft. Anterior anal spines rather small. 
Branchiostegal rays, five. Bluish grey above ; sides silvery. Dorsal and caudal greyish yellow ; anal, ventrals, and pectorals, 
dull yellowish. 
Syn. —Amphistichus similis, Grd. in Proc. Acad. Nat. Sc. Philad. VII, 1854, 135 ; and, VII, 1855, 323. 
This species is very closely allied to the preceding one and, mayhap, not distinct from it. 
The great disproportion in size between the specimens described, and the fact of their belonging 
to different sexes, is not calculated to facilitate the comparative study of their specific identity 
or difference. Thus the more elongated shape of A. similis may not be a character constant 
throughout the entire range of growth. The same remark may be applied to the shape of the 
snout and the extension of the maxillar bone. Yet the latter trait we find on another 
specimen one-third larger than the one figured and apparently a male. Now, on both male 
and female of what we consider as A. similis, we find the spinous portion of the dorsal fin of 
the same height as the soft portion, with a depression in the outline between the two. The 
latter feature we would consider as a very important character, since we know by the study of 
the embryo that the spinous portion is of a more tardy development than the soft; now, finding 
that portion of the fin proportionally higher in a specimen of A. similis , much smaller than A. 
argenteus, we were necessarily led to draw a specific distinction between the two. The anal 
spines, we are inclined to think, are more developed in the male than in the female of the same 
species, and consequently the value of this character is to be subjected to renewed observations 
on a more complete series of individuals. We find but five branchiostegal rays on either 
side in A. similis, whilst A. argenteus has six of them. 
The base of the anal enters exactly five times in the total length. The caudal constitutes 
less than the fifth of the length. The origin of the ventrals is situated under a vertical line 
