324 THE ENTOMOLOGIST. 



presents itself is the general uniformity of their colouring ; 

 all have the head and thorax black ; the abdomen red, with 

 the apex more or less black ; the base of the abdomen is 

 also black in the females of one or more species. The 

 colouring of the abdomen varies most in the males ; in 

 S. ephippia a variety totally black is sometimes found. 

 Colour therefore cannot be relied upon as a means whereby 

 to discriminate the species. The constant and marked dif- 

 ferences which present themselves in form and sculpture 

 render the separation of the species a matter of very slight 

 difficulty. 



In the spring, only females of these bees are to be found, 

 but as the summer advances males also appear, and during 

 the autumnal months both sexes are usually very abundant. 

 S. subquadralus is, however, rare, and 1 do not know any 

 precise locality for S. fuscipennis. 



It has been found that the difference of form in the gene- 

 rative organs of the males of various species of wasps, bees, 

 and of some species of fossorial insects, presents perfectly 

 reliable characters for the separation of species ; this test 

 cannot however, unfortunately, be applied to the males of all 

 the species of bees, but it can be used in the genus Sphe- 

 codes. After a careful examination of these organs in all 

 our British species, I find such constant and distinctive dif- 

 ferences that I am quite convinced of the specific difference 

 of ihe five species enumerated in this paper. The organs of 

 a number of examples of each species have been examined, 

 and careful drawings made of each, which present constant 

 and excellent specific characters. 



I will in the next place endeavour to point out such 

 specific differences as will serve to separate the females of 

 this genus. Sphecodes gibbus has the head considerably 

 wider than the thorax ; this is not the case in the other 

 species ; the head is also of a different form behind the eyes, 

 the sides being very abruptly rounded or sloped off. The 

 disk of the thorax of S. gibbus is very polished and shining, 

 with punctures wide apart ; ihe punctuation of the thorax of 

 S. rufiventris is very much closer, and is thereby rendered 

 semi-opaque ; this species is also distinguished by having at 

 the base of liie metalhorax a semicircular space enclosed by 

 an elevated ridge, whilst in S. gibbus the ridge is obsolete. 



