The existence of two strains or varieties of Aropheles crucians was first noted by Root (1). The distinguishing characteristics of these varieties are detectable only in the fourth larval instar, the imagines being undifferentiable by any known criteria. One strain favors fresh water, the other brackish water, and consequently they are referred to as the inland and the coastal varieties respectively. Root noted that the larvae of the coastal variety agreed with the published descriptions of the larva of this species, and possessed five pairs of palmate hairs, while the hitherto undifferentiated larvae of the inland variety resembled those of A. quadrimaculatus in so far as the palmate hairs (six to seven pairs) are concerned. Bradley (2) appears to be the only other entomologist who has studied the differentiation of the races of A. crucians. He found that the larvae of the inland variety possess the characteristics of A. crucians distinguished by Russell (3), namely two hair tufts anterior to the palmate hairs on the fourth and fifth abdominal segments.