122 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 9 



Notes on geographical variation. — ^We have been considerably dis- 

 turbed by the differences which exist between our Arroyo de San Luis, 

 Lower California, material of E. eriarcha and the series from the coast 

 of Oaxaca. Except for two rather peculiar examples, one from each place, 

 and two or three small, less well-preserved individuals, the series from 

 the two localities are separable upon veiy superficial examination. In the 

 Lower California fish the predorsal profile of the back is flattened, the 

 dorsal contour being broken at the origin of the second dorsal fin and 

 thence sloping in a concave curve to the caudal fin. The head of the fish 

 seems to be more definitely in line with the straight axis of the body {i.e., 

 the head axis in line with the body axis), and the eye to be placed in line 

 with the body axis. In the Oaxaca specimens, on the contrary, the pre- 

 dorsal profile of the back is definitely arched, there is little or no break 

 in the dorsal contour at the origin of the second dorsal fin, and the profile 

 posterior to this point is straight or only slightly concave back to the nar- 

 rowest part of the caudal peduncle. The head axis is definitely at an angle 

 with the less-straight body axis, the head appearing to be pointed slightly 

 downward, and the middle of the eye is definitely below the front part of 

 the body axis. Moreover, the Oaxaca fish seem to have a somewhat more 

 pointed and less pigmented snout when viewed from above, the top of the 

 head is less flattened, the dark scale-edging of the back is usually weaker 

 and sometimes absent, and the preventral profile is more oblique and less 

 liable to be horizontal than in the Lower California individuals. 



The differences in appearance caused by these features are striking 

 in almost all the specimens of the two series, but are difficult to reduce to 

 definitive descriptions. Perhaps the most easily expressed difference is the 

 position of the eye in relation to straight lines projected forward along 

 the lines of the anterior upper and lower borders of the lateral silvery 

 band. In the Lower California series the projected line of the upper edge 

 of the band subtends the upper part of the pupil, while in the Oaxaca 

 specimens the same projected line passes entirely above the orbit or sub- 

 tends only the uppermost part of the rim. 



These characters are, however, all variable, and no one of them is 

 entirely constant for the locality. Moreover, we have been unable to apply 

 these character-criteria with any degree of precision to the available ma- 

 terial from localities other than Lower California and Oaxaca, chiefly 

 because all these other specimens are in much poorer condition than the 

 magnificently preserved series obtained by Dr. Bolin. Finally, it seems 

 extremely unlikely that the single original type of eriarcha from Mazat- 



