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 

 in 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. 



2. AMPHISTICHUS SIMILIS, Grd. 

 PLATE XXXYI, Figs. 6-9. 



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. Bluiih grey above ; sides silvery. Dorsal and caudal greyish yellow ; anal, ventrals, and pectorals, 

 dull yellowish. 



S. 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 



