AMERICAN HYMENOPTERA. 187 



SYNOPSIS OF AIKDREIVIN^. 



BY CHARLES ROBERTSON. 



Since the publication of the synopsis of the local species of 

 Andrena, in Trans. Am. Ent. Soc, xviii, 49, 1891, quite a number 

 of species have been added, some mi.-sing sexes have been found, as 

 well as some characters which may be useful in separating the spe- 

 cies. I feel quite responsible for the things to which I have giveu 

 names, and I hope that the following table will facilitate their recog- 

 nition. All of the characters used here have been used before in 

 my descriptions of different species. 



The group is so heterogeneous that it ought to be divided into 

 several genera. Its size would justify this, even if it could be shown 

 that the genera are of less than ordinary validity. 



Unless otherwise indicated, enclosure ^ the enclosed space at 

 base of metathorax ; fovea =: facial or supraorbital fovea ; process 

 = basal process of labrum ; vein III5 = 2nd transverse cubital nerv- 

 ure ; vein IV3 = 1st recurrent nervure ; vein IV2 = 2nd recurrent 

 nervure; cell III1+2 = marginal cell; cell III5 = 2nd submarginal 

 cell; cell III4 = 3rd submarginal cell; "joint" refers to antenna; 

 "segment" refers to abdomen. 



FEMALES. 



Enclosure strongly rugose, usually bounded by salient rim, usually truncate; 

 sides of segment 2 less widely depressed, more or less gibbous, with 

 a small fovea ; joint 3 shorter than 4-}- 5 ; outer face of hind tibia with 

 simple hairs Trachandrena. 



Enclosure triangular, defined by impressed line or by absence of hair, usually 

 continued to a point on posterior face, not so strongly rugose ; joint 3 

 usually as long as, or longer than, 4 + 5 1. 



1. Hairs on outer face of hind tibia plumose 4. 



Hairs on outer face of hind tibia simple 2. 



2. Glossa filiform, pubescent ; labial palpi long, joints subequal ; clypeus produced ; 



cheek broad behind summit of eye ; joint 3 = 4-6 lonielissa. 



Glossa as usual ; labial palpi short, joints unequal 3. 



3. Vein III5 present Andrena or 0|>an<lrena. 



Vein III5 absent; process small, triangular Paruudrena. 



4. Tibial scopa thin, thinly plumose Ptilaiidreiia. 



Tibial scopa dense, densely plumose Pterandrena. 



TRANS. AM. ENT. SOC, XXVIII. JUNE, 1902 



