Czl £2-S~ PROCEEDINGS CALIFORNIA ACADEMY OF SCIEN&ES? Fourth Series Vol. XI, No. 16, pp. 345-393, 30 text figures December 31, 1921 XVI REVISION OF THE PIPIZA GROUP OF THE FAMILY SYRPHLDiE (FLOWER-FLIES) FROM NORTH OF MEXICO BY C HOWARD CURRAN Orillia, Ontario, Canada The genus Pipiza, as generally accepted in North America, has long been regarded as one of the most difficult genera in the family. The reason for this is found in inadequate descriptions and the absence of outstanding specific characters which could be used for identification. Abundant material has revealed several characters which are of exceptional importance in this group and the old reliance upon the color of the pile is not adhered to in this work where other characters are sufficiently prominent to allow of their employment. The character of the pile often indicates species and is of considerable importance, as variation is not as great as is generally supposed. Many small differences usual-ly accompany its variation in color, and these, together with more important structural differences, lead to the absolute determination of the specimens. The present paper deals with forty-nine species of North American Pipizini. Their retention in a single December 31, 1921
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