Two geographic races each of Salveli?zz~s fontinalis and S. alpifzz~s respectively were co~nparcd \\.it11 respect to their upper lethal temperatures and the efect of temperature on cruising speed. The two races of S. fontinalis, which arc not recognized n~orphologically as subspecies, could not be separated on the basis of these tests. A dilference in the upper lethal temperatures was found between the two groups of S. a l p l~~z~s , which are recognized as subspecies. No dilfcrcnce was found in thc response of the cruising speed t o temperature, however.One sample came from Lalce Windermere, England, a small, almost oligotrophic lake where the stoclc is recognized as S. a. willughbii (Gunther).The other came froin a large oligotrophic lake, Lake Geneva, France, and is linowil as S. a. alpinus (Linn.).'Manuscript received M a y 17, 1957. Contribution from the Department of Zoology, University of Toronto, Toronto, Ontario. This DaDer is based uDon a thesis submitted in ~a r t i a l fulfillment of the reauirements for the d e g r k df Master of i r t s a t the University of oro onto.