( 21) 
petiolated, the petiole being an elongation of the first seg- 
ment, very rarely a distinct articulation (Ammophila vul- 
garis and Miscus), frequently apparently distinct, but not 
so (Psen, Mimesa, Ammophila, Stigmus, Pemphredon and 
Cemonus). It is generally longer than the thorax, rarely of 
the same length (female Wethoca, Crabro brevis), and only 
in the instance of the male Astata boops shorter; it is ge- 
nerally elongate, ovate, and acuminate, at its apex, but in 
male insects frequently obtuse or truncated; it is rarely 
linear (male, Methoca), or clavate (Ammophila and Miscus), 
sometimes ovato-conic (Vysson, Gorytes, Oxybelus), and oc- 
casionally sub-clavate in Trypoxylon, and in some species of 
Crabro, in the latter genus frequently subcuneiform, but 
rarely triangular (Astata). The segments are subcoarctate 
in Oxybelus and Dolichurus, and fully so in Cerceris. The 
second ventral segment is produced anteriorly in Vysson, 
more slightly so in some species of Gorytes; the terminal 
ventral segments are emarginate in the males of some species 
of Pompilus, and the hypopygium in the male Methoca and 
in Ziphiais prolonged into a compressed upcurved spine; 
the last segment is truncated in the males of Vysson, Ta- 
chytes, and Larra, with two small processes at its lateral 
extremities, and in Ceropales an ovipositor is exserted. 
This last is the only instance of an ovipositor being exserted 
in an aculeate Hymenoptera. 
§ 5. 
My observations here upon the economy and habits of 
these insects will be very brief, as it would be merely an 
unnecessary repetition, for under each species will be 
found all that has as yet been observed; I may refer to my 
paper on the subject in the Entomological Transactions* 
* Vol. i. part I, p. 52. 
