I 



1917.] NATURAL SCIENCES OF PHILADELPHIA. 305 



COLPICHTHYS, THYRINOPS. AND AUSTROMENIDIA, 

 New Genera of Atherinoid Fishes from the New World. 



BY CARL L. HUBBS. 

 COLPICHTHYS new genus. 



Genotype. — Atherinops regis Jenkins and Evermann (Gulf of 

 California) . 



Colpichthys regis is related to the species of Atherinops, with which 

 it has heretofore been considered congeneric. But the Gulf species 

 differs in so many ways from the typical species from the outer 

 coasts of Lower California, and from California and Oregon, that a 

 new genus may be erected for its sole reception. 



Compared with Atherinops, Colpichthys may be distinguished as 

 follows. The head is depressed, although the body is deeper and 

 more strongly compressed than in Atherinops. The mouth is sub- 

 inferior, being on a level with the lower margin of the eye; the upper 

 lip is thickened. The uniserial teeth are Y-shaped, but the inner 

 fork is usually much the shorter. The gill-rakers, 16 to 18 in number 

 along the lower limb of the outer arch, are strongly compressed, 

 curved, serrate on their inner margins, and relatively short, being 

 about one-fourth as long as the eye. In typical Atherinops the gill- 

 rakers are rather more numerous, 20 to 25, and they are slender, 

 terete, straight, nearly smooth, and about two-fifths as long as the 

 eye. 



The scales of Colpichthys differ markedly from those of Atheriiiops, 

 although constructed on a similar plan. The posterior or exposed 

 field of the scale is marked outward from the focus to the first annulus 

 or seasonal ring by circuli similar to those of the anterior field, but 

 beyond this mark the circuli assume a sharply and irregularly undu- 

 late course paralleling the posterior margin of the scale. In 

 Atherinops proper {A. affinis) the circuli of the po.sterior field through- 

 out maintain a nearly even course, and are all greath" crowded, while 

 in Colpichthys only those in the annuli or year checks are closely 

 approximated. In Colpichthys there are about six basal radii within 

 the first annulus, beyond which the number is abruptly decreased. 

 In Atherinops, on the other hand, the radii are often absent, but on 

 some scales 1, 2, or even 3, are in' evidence; and these radii are not 



22 



