CLASSIFICATION OF THE BEES. 87 



The three cubital cells in the front wings, as well as usually the 

 much shorter tongue, separate them from the Panurgidse, which 

 have only two cubital cells. Some Panurgid genera, however, have 

 also short tongues and are in no way to be distinguished from the 

 Andrenids, except in having only two submarginal cells. They are 

 evidently recent offshoots from an Andrenid stock. 



The family may be separated into three subfamilies as follows : 



Table of Subfamilies. 



First branch of basal nervure always strongly curved or bent inwardly, funn- 

 ing a segment of a circle ; epimera of mesothorax well separated, dis- 

 tinct 2. 



First branch of basal nervure straight or very nearly, never strongly curved 

 inwardly ; epimera of mesothorax not or scarcely separated ; hind 

 tihise in both sexes with a knee plate- • .Subfamily I. Andrenin.e. 



2. Hind femora and tibia? in 9 with a distinct flocculus or scopa, the ventral 

 scopa sparse, but distinct; fifth abdominal segment always with a 



rima Subfamily II. Halictin^:. 



Hind femora and tibia? in 9 without a distinct flocculus or scopa, when present 

 very sparse and thin, and scarcely noticeable ; fifth abdominal segment 

 without a rima ; venter bare Subfamily III Sphecodin^:. 



Subfamily I. Andrenin.e. 

 The bees belonging to this group are exceedingly numerous and 

 common, appearing very early in the Spring and lasting all during 

 the Summer months, being most active in nest building during the 

 months of June and July. Their nests are made in burrows or 

 tunnels in the ground or in hard clay banks, preferably the latter. 

 The tongue in all the genera is short and triangularly pointed, the 

 labial palpi 4-jointed, the maxillary palpi usually 6-jointed, while 

 the basal nervure is straight or nearly, never curved or strongly bent 

 inwardly, as in the Halictime and the Sphecodina? ; the scopa on the 

 hind legs, in 9 , being always distinct, well developed. 



Table of Genera 



Front wings with three cubital cells. 



Marginal cell at apex acuminate or narrowly rounded, never truncate- . . -4. 

 Marginal cell at apex obliquely truncate and usually with a short appendage 



(or stump of a vein) from the lower angle 2. 



2. First cubital cell, along the cubitus, as long as the second and third united or 



nearly • • 3. 



First cubital cell, along the cubitus, about as long as the third, the latter nar- 

 rowed one-half above along the radius, and receiving the second recur- 

 rent nervure far beyond its middle; second cubital cell quadrate, re- 

 ceiving the first recurrent nervure beyond its middle; head very 



TRANS. AM. ENT. SOC. XXVI. JUNE, 1899. 



