Abstract
A survey of salivary gland chromosomes of larval Prosimulium revealed a. group of seven west coast species that form a natural unit by virtue of sharing arrangement IIIL-2 in the long arm of chromosome III. Detailed band comparison showed that the Alaskan species P. frohnei Sommerman and P. hirtipes E belong together on one line of descent while P. fulvum (Coquillett), P. hirtipes 2 (Alaska), P. travisi Stone, P. formosum Shewell, and P, "species 1" belong to another branch.