6. (XELIOXTS. 141 



cells, the second receiving both the recurrent nervures, the first near 

 its base, the second near its apex. Abdomen conical, its base trun- 

 cate and its apex acute ; in the males the apex is obtuse and toothed. 

 The claws simple in the females, and bifid at their apex in the males, 

 which have the anterior coxa? toothed. 



This genus is one of considerable extent ; about sixty species are 

 known, only six of them being found in Great Britain ; some species 

 are widely spread throughout Northern Europe, being found in Russia, 

 Sweden, and Siberia. Twelve species are known from Africa, having 

 been found in Guinea, on the Gambia, in Angola, and at the Cape of 

 Good Hope ; about twenty are Asiatic; and thirteen are known from S. 

 America, and rather more than that number from X. America. It is 

 singular that this genus has not been discovered in Australia, since the 

 genus Megachile, upon which it is principally parasitic, is common 

 in that country ; some of the species are parasitic on species of 

 Saropoda. These bees by no means confine their attacks to the 

 nests of one species of JJer/ackile : C. vectis is frequently parasitic 

 on M. maritima, but it also attacks 31. willughbiella ; G. simplex is 

 at one time parasitic on 31. circumcincta, and at another on 31. argen~ 

 tata. Great difficulty attends the discrimination of the males of the 

 different species, whilst the differences in the form of the apical 

 ventral plates of the abdomen of the females render their indentifi- 

 cation comparatively easy. Much confusion has arisen in the 

 synonyma of this geuus, in consequence of different authors having 

 been unable to distinguish the typical species described by Linnseus, 

 each sex being accounted as distinct by that author. The types of 

 Linnaeus being preserved in his cabinet in the collection of the 

 Linnean Society, I hope by a careful examination of them to remove 

 the difficulty. Foerster has thrown the genus into a chaos of con- 

 fusion by his system of making species upon the slightest differ- 

 ences. In all species of bees, but more particularly such as are 

 parasitic on more than one species, great discrepancy in size aud 

 also in the development of parts must be always taken into con- 

 sideration. The most variable species of the genus found in this 

 country is C. simplex, which I have found to vary in length from 

 3f lines to 6| lines ; the smaller examples have the lower valve of 

 the anal segment of the abdomen very narrow and acute at the apex, 

 but a gradual approach to this is to be traced in a good series of ex- 

 amples. C. vectis appears to be the most uniform in size and structure. 



All the British species of this genus emit, when captured, a very 

 offensive odour. Probably they can do this voluntarily : if so, it may 

 preserve them from the attacks of birds, or from molestation when 

 in the act of ovipositiou in the nests of the industrious bees upon 

 which they are parasitic. 



2. Ccelioxys quadridentata. 



G. atra ; scutello utrinque dentato, margine postico obtuse subangu- 

 lato ; abdomine conico, segmentis margine albidis ; ano maris den- 

 tato, calcaribus posticis nigris. 



