Species Structure of the Gobiid Fish Gillichthys mirabilis from Coastal Sloughs of the Eastern Pacific'

A RECENT ISSUE of Systematic Zoology (1960, vol. 9, nos. 3, 4 ) was ' devoted entirely to a symposium entitled "The Biogeography of Baja California and Adjacent Seas." One recurring theme was the affinity between forms occurring on the Pacific Coast in the Californian province (Hubbs, 1960: 134), and those in the northern part of the Gulf of California. Between these areas, in the main part of the Gulf, the fauna was said to differ, being primarily Panamic in origin (Garth, 1960; Hubbs, 1960; Walker, 1960) . The outer-coast species found in the upper Gulf of California are Pleistocene relicts , now trapped in a cul-de-sac of warm , tropical water (Hubbs, 1948 : 463 ; 1960 : 137) . According to Walker (1960 : 130) , most of the northern species found there differ from their cognates on the Pacific Coast. As the symposium revealed, however, there has been no extensive study comparing populations of one species on the Pacific Coast with those of the same species in the Gulf of California. The immediate objective of this investigation , although it was initiated before the symposium was conceived , was to establish the nature of the variation between populations of Gillichthys mirabilis Cooper. The goal was to ascertain the degree of differentiation of the form from the upper Gulf in relation to the over-all structure of the species. A brief study ( Barlow, 1961a ) of G. seta ( Ginsburg) has served as comparative material to gauge the differences observed in G. mirabilis. G. seta is a close but distinct species restricted to an ex-