The MALE scarcely differs, excepting that the whole of the front of the head is more densely pubescent; the mandibles are deeply, acutely, and nearly equally tridentate, the terminal segment of the abdomen is variously mucronated or toothed at its apex, these processes pointing backwards, and the penultimate segment is more or less produced laterally. NATIVE SPECIES. 1. _conica_, Linnæus, ♂ ♀. 4-5 lines. _quadridentata_, Linnæus, ♂. _quadridentata_, Kirby, ♂. 2. _simplex_, Nyland, ♂ ♀. 5 lines. _conica_, Kirby. _conica_, Curtis, viii. 349. _Sponsa_, Smith, ♂. 3. _umbrina_, Smith, ♂ ♀. 4. _rufescens_, St. Fargeau, ♂. 4-6 lines. 5. _vectis_, Curtis, ♂ ♀. 5-6 lines. (Plate XII. fig. 1 ♂ ♀) 6. _inermis_, Kirby. GENERAL OBSERVATIONS. This genus is named from _κοιλία_, _belly_, _ὀξὺς_, _acute_, in application to the conical abdomen of the female. The insects of this genus are parasitical upon the genera _Megachile_ and _Saropoda_. Thus, _C. simplex_ infests _M. circumcincta_; _C. rufescens_, _M. Willughbiella_; _C. vectis_, _M. maritima_; and _C. umbrina_ is parasitical on _Saropoda bimaculata_. Linnæus, from the different appearance of the two sexes made two species of them, and from the circumstance of his having described first the male as _Apis quadridentata_, this, by the law of priority, supersedes the name of _C. conica_ as the name of the species, which is its female, and which he next described, and thus that sex, whose form Latreille adopted as typical of the genus, is in the series of species totally superseded and reduced to a synonym. The species of this genus are extremely difficult to separate from each other, no tangible character presenting itself conspicuously, although the Swedish entomologist Nylander supposes he has found one in the plates of the apical segment of the abdomen, especially those of the venter, in which he detects both a difference of form and a difference of relative length to that of the superior plates, and in the males he assumes that the teeth of the apical segment are constant characters. Not having had sufficient opportunity since this supposed discovery was made, for the examination of a great multitude of specimens, for it is only upon such an investigation that it can be firmly based, I cannot speak corroboratively upon the point, but it is very possibly a correct solution of the difficulty.