( 15 
disparity in the form of the mandibles, for in the male they 
are particularly strong, and approach much to those of the 
genus Pemphredon ; in the genus Diodontus also there isa 
sexual difference. The processes or teeth are generally 
apical, yet we sometimes observe them basal internally, as 
in some Crabros and in Tachytes ; and in the latter genus 
and JLarra, &c. there is an external process towards the 
base. The form which most generally obtains is bidentate, 
with the exterior tooth the longest; but in some, as in the 
Crabros, it is the shortest; in some however it is unidentate 
and acuminate at its apex. When closed they are fre- 
quently forcipate ; they then pass over the labrum, and thus 
inclose the whole internal cibarial apparatus. The interior 
PALPI are always four jointed and the exterior six, they vary 
much in their form both in the genera and species. The 
TONGUE, which I consider to be that portion of the cibarial 
apparatus, which is thrust forward to lap the nectar of 
flowers, or as it is more apparent in the bees, the hairy tube 
through which they suck it, is in this tribe very variously 
formed—sometimes indeed it is so short as to be scarcely 
evident; in Tiphia, it is very short and rounded, it is very 
generally bifid or emarginate with the lateral edges reflect- 
ed; in Ammophila, it is elongate, still bifid, and in closing 
reflected backwards, which induced Mr. Kirby to consider 
that this genus ought to come near the bees. This circum- 
stance strongly exhibits a prominent defect of the cibarial 
system, as it would bring together insects of so great a dis- 
parity of habit and economy. In Crabro, it is truncated 
anteriorly and laterally produced, and to this form Oxybelus 
closely approaches. In Pompilus, it is trilobate, the lateral 
lobes having each, near their base, a pilose spot. In Phi- 
lanthus, it is deeply emarginate, and the sides are produced 
into pilose angles. 
