CHARLES W. METZ. 



95 



in this way only can the sexes be associated with certainty. 

 In cyanide cans the yellow markings may turn to orange, 

 but no harm is done, for the shade of color is usually of no 

 value anyway. 



The breeding and rearing of specimens offers a very attrac- 

 tive field in this genus, and may solve some of the most in- 

 tricate problems. In this way it can be determined whether 

 some of the species are really distinct, or whether the females 

 that are so similar are of one species and have polymorphic 

 males. At present there is no way of ascertaining this, but 

 from the indications it is not at all improbable that such a 

 condition exists. If so it will greatly simplify matters to 

 have accurate knowledge of just where, and to what extent 

 this is true. Nests of Prosopis containing larvae or pupae 

 can often be found in the hollow dead stalks of many com- 

 mon pithy weeds or canes, and it is to be hoped that col- 

 lectors will take pains to obtain such material whenever 



possible. 



Genus PROSOPIS, Fabricius. 



Generic characters. — Tongue short, broad, obtuse, emargin- 

 ate at apex. Marginal cell at apex acuminate or narrowly 

 rounded, never truncate. Body bare or nearly so. First 

 cubital cell much longer than second. Maxillary palpi six 

 jointed ; labial palpi four jointed. Usually small black bees 

 with yellow markings. 



In America bees of this genus are easily recognized by 

 their black color, small 



size, absence of pubes- \y -^~^_Z-'^ V 



cence, and presence of yel- 

 low markings, together 

 with the short tongue and 

 two cubital cells. The 

 mouth parts apparently 

 show no variation what- 

 ever, that could be used 

 in specific diagnosis. A 

 series of twenty or thirty 

 mounts from different species are identical in form and agree 

 essentially with the figure given, (fig. 2). 



TRANS. AM. ENT. SOC, XXXVII. 



