The more important of the groups that have been recognised are—(1) the Obtusilingues, short-tongued bees, with the tip of the lingua bifid or broad; (2) Acutilingues, short-tongued bees, with acute tip to the tongue; these two groups being frequently treated of as forming the Andrenidae. Coming to the Apidae, or the bees with long and folded tongues, there have been distinguished (3) Scopulipedes, bees carrying pollen with their feet, and (4) Dasygastres, those that carry it under the abdomen; some of the parasitic and other forms have been separated as (5) Denudatae (or Cuculinae); the Bombi and the more perfectly social bees forming another group, viz. (6) Sociales. A group Andrenoides, or Panurgides, was also proposed for certain bees considered to belong to the Apidae though exhibiting many points of {21}resemblance with the Andrenidae. This arrangement is by no means satisfactory, but as the tropical bees have been but little collected, and are only very imperfectly known, it is clear that we cannot hope for a better classification till collections have been very much increased and improved. The arrangement adopted in Dalla Torre's recent valuable catalogue of bees[19] recognises no less than fourteen primary divisions, but is far from satisfactory. [Illustration: Fig. 10—_Prosopis signata._ Cambridge. A, Female; B, front of head of female; C, of male.] The two genera _Prosopis_ and _Sphecodes_ have been recently formed into a special family, Archiapidae, by Friese,[20] who, however, admits that the association is not a natural one. The term should be limited to _Prosopis_ and the genera into which it has been, or shortly will be, divided. The primitive nature of the members of this genus is exhibited in all the external characters that are most distinctive of bees; the proboscis (Fig. 9, B, C), is quite short, its ligula being very short, and instead of being pointed having a concave front margin. The body is almost bare, though there is some very short feathered plumage. The hind legs are destitute of modifications for industrial purposes. Owing to these peculiarities it was for long assumed that the species of _Prosopis_ must be parasites. This is, however, known not to be the case so far as many of the species are concerned. They form cells lined with a silken membrane in the stems of brambles and other plants that are suitable, or in burrows in the earth, or in the mortar of walls; individuals of the same species varying much as to the nidus they select. The food they store in these cells is much more liquid than usual, and has been supposed to be entirely honey, since they have no apparatus for carrying pollen. Mr. R. C. L. Perkins has, however, observed that they swallow both pollen and nectar, brushing the first-named substance to the mouth by aid of the front legs. He {22}has ascertained that a few of the very numerous Hawaiian species of the genus are really