234 Rev. F. D. Morice on Armatures, etc. of A7tdrcna. 



form. In several of the ' lateral views ' letters are used to 

 show X the ' geniculation,' and y the tooth-like end of the 

 ' thickening ' in the process. 



In Fig. 5 the constriction of the base into the process is 

 gradual, in Fig. G it is sudden, and in Plate VII, Figs. 1 

 and 2, it gives the basal plate a ' shouldered ' appearance. 



In Plate VI, Figs. 9a and 13fi, the geniculation is more 

 or less ' lobate,' the lobe in each case being indicated by 

 the letter x. [By, comparing in succession a series of 

 lateral views of different species (3a, Qa, la, loci, 12a, 11a, 

 10a, 9a), we can trace the gradual development of a hardly 

 sensible geniculation into the conspicuous projection, which 

 gives so curious a character to the apex of the valvula 

 vcutralis in many species, of which labialis, Kirby, is the 

 only British example.] 



Having thus defined the terms I shall have to use, I 

 will say at once what remains to be said as to the terminal 

 characters which my figures are meant to illustrate. 



1. The armatures (Plate V). 



What seems to me most of all to determine the general 

 look of an Andrena armature is the apical outline (c d) of the 

 lobe. Whenever this is deeply sinuated inwards the lobe 

 becomes distinguishable at a glance from such simple forms 

 of it as appear in my first two or three figures. The actual 

 effect produced in each case depends (1) partly on the 

 depth of the sinuation, making the tooth-like angles longer 

 or shorter, (2) partly on the more or less near approach of 

 the sinuation to the interior margin, making the teeth 

 look broader or narrower, and (3) partly on the duration 

 of the curve {i.e., its approximation to a completed circle), 

 making them more (Fig. 19) or less (Fig. 20) divergent. 

 But in all these cases, the lobe ' looks dentate ' to an 

 extent which catches the eye at once after a little practice. 

 It is instantly distinguishable from the merely acute- 

 angled lobe with simple outline show^n in Fig. G ; and still 

 more from the right-angled, or the (rare) obtuse-angled 

 types of lobe, of which Figs. 4 and 9 respectively are 

 examples. 



Again, a decided S-like sinuation (as in ovina, Klug, 

 Fig. 15) gives the lobe an oval or dome-like character, 

 which can be recognised at a glance. Even a slight S-like 

 sinuation (Figs. 14 and 17) produces something of this 

 effect. 



Next to these differences in the apical outhne, those of. 



