EXTERNAL ANATOMY OF INSECTS. 633 



expressed, according to the number of their areolets; by 

 figures, the protomesal standing first. They vary much 

 in this respect in the different genera. Thus in Cyclo- 

 stoma K. a , reckoning the didymous areolet as two, the 

 numbers will stand 4:2:1; in Hylotoma, &c, 3:2:l b ; 

 in Aulacus, &c, 2:2: l c ; in Bracon, &c, 2:l:l d ; in 

 Chelonus, 2 : : 1 e ; in Cynips erythrocephalus Jur., 2 : : f ; 

 in Formica, 1:1:1?; in Oxybelus, 1 : : 1 h ; in Chrysis, 

 0:1:1"; and in Cynips Rubi K., l:0:0 k . The most 

 natural number is 3:2:1. The next in importance to 

 the medial areolets of the Intermediate Area are the 

 apical, or those open to the margin ; the most usual num- 

 ber of them, excluding the postcostal areolets which be- 

 long to the Costal Area, is three ; but in Sirex there is 

 an approach to four ' ; in Evania there are only two m ,- 

 and in Philanthus there are none n ; in many, as Proso- 

 pis, Nomada, Andrena , though there is the usual num- 

 ber, they are incomplete and do not reach the margin. 

 The basal areas are of little importance in assisting to 

 determine genera; they are most commonly two in num- 

 ber, but in Cynips, &c, there is only one p . The shape 

 and other circumstances of the areolets vary consider- 



a This is a remarkable insect belonging to Vespa L., related to the 

 hornets ( V. Crabro), distinguished by having a semicircular piece taken 

 out of the internal margin of each mandible, so that when these or- 

 gans are closed there is a circular orifice, — whence the name Cyclo- 

 stoma. b Jurine Hymenopt. t. ii. Gen. 2. c Ibid. Ord. ii. Gen. 2. 



•' Ibid. t. iii. Gen. 3. e Ibid. t. v. Gen. 41. 



'" Ibid. t. xii. Gen. 40. g Ibid. t. v. Gen. 39. 



h Ibid. I. iv. Gen. 29. ; Ibid. t. v. Gen. 42. 



k This Cynips inhabits a long polythalamous gall of the bramble. 



I Jurine "ibid. t. ii. Gen. 11. ' m Ibid. Ord. ii. Gen. 1. 



II Ibid. t. iv. Gen. 23 ° Ibid. Gen. 30—32. 

 p Ibid. t. v. Gen. 40 



