17? HYMENOPTERA ACULEATA. 



Prosopis and Culletes having bifid tongues like tlioso of tlie 

 Diploptera and Fossores. There are two points of structure 

 which may be relied upon as characteristic of this section 

 throughout ; these are the dilated posterior metatarsi, and 

 the plumose hairs of the thorax ; the former of these 

 characters is somewhat indistinct in the (^ of Andrena, and 

 of some other genera, but the latter, at least so far as the 

 British species are concerned, is always reliable, and only 

 requires sufficient magnifying power to disclose it. So far 

 as I have been able to examine exotic species, it also holds 

 good, but to this, like all other single characters, these are 

 probably exceptions, and it is in combinations of peculiarities 

 of structure as well as of habits that we have to seek satis- 

 factory characters of a sectional nature. The generic 

 characters in the Anthophila are chiefly derived from the 

 tongue and mouth parts ; these appear to be very constant, 

 and differ much in the various genera. Some genera, like 

 Halictus and Sphecodes, have short tongues, no distinct 

 lora, and cylindrically-jointed labial palpi ; others, like the 

 higher Ajndx, have long tongues, well developed lora, 

 and sheath-like labial palpi which fold over the tongue. I 

 think it is clear that the Ohtusilinguse should immediately 

 follow the Dqjloptera, but beyond that it is almost impossible 

 to make any satisfactory linear arrangement. Such genera 

 as Colletes, Rhophites, Panurgus, Nomada, Macrojns, and 

 Ceratina upset any scheme which one can invent. It is 

 not therefore because I think the present arrangement 

 satisfactory that I adopt it, but simply because I cannot 

 suggest a better. 



The Anthophila may be thus characterized : — Species 

 social or solitary. If social, communities consisting 

 of male, female, and worker, except in the case of 

 Psithyrus (the messmate of the Humble Bee), where no 

 worker occurs ; tongue short and bifid, short and pointed, 

 or elongate and filiform, with or without a terminal en- 

 largement ; labial palpi generally 4-jointed, cylindrical, or 



