The FEMALES of the second division of the genus scarcely differ.
The MALES of the first division differ in having the _head_ slightly larger and squarer above; the _antennæ_ very slightly longer; the _mandibles_ more acutely tridentate, with a distinct powerful basal tooth beneath, terminating the concavity of the organ; the anterior _femora_, _tibiæ_, and joints of their _tarsi_, excepting the terminal one, concavo-convex, the four first joints of the latter distended laterally, and edged with a dense fringe of setæ, the distension of these joints is widest at their articulation with the tibiæ and they decline in length to the claw-joint which is long; the _claws_ bifid; the interior claw acute, but remote from the apical one; the posterior _femora_ are very robust, their _tibiæ_, much curved, robust, almost triangular, and externally very convex; their _plantæ_, almost glabrous, not so long as the three following joints, externally rather twisted, and beneath furnished with a dense brush of long stiff hair.
In the second division of the genus the males are destitute of the distension of the anterior tarsi, these being instead densely fimbriated externally; the legs in them are much less robust, and more closely resemble those of their females.
§ _Anterior tarsi of males much dilated._
1. _Willughbiella_, Kirby, ♂♀. 5-7 lines. 2. _maritima_, Kirby, ♂♀. 6-7 lines. (Plate XII. fig. 2 ♂♀.) 3. _circumcincta_, Kirby, ♂♀. 4½-5½ lines.
§§ _Anterior tarsi of males not dilated._
1. _ligniseca_, Kirby, ♂♀. 5-7 lines. 2. _centuncularis_, Linnæus, ♂♀. 4-6 lines. _centuncularis_, Kirby. 3. _argentata_, Fabricius, ♂♀. 3-4½ lines. (Plate XII. fig. 3 ♂♀.) _Leachella_, Kirby. _Leachella_, Curtis. 4. _odontura_, Smith, ♂. 4½ lines.
Named from the great development of the labrum, _μέγα_ _large_, _χεῖλος_ _lip_, which is characteristic of all the _Dasygasters_, and also of some of the proximate _Nudipedes_, those parasitical upon them, _Stelis_ and _Cœlioxys_, and which, too, resemble the sitos in the expansion and dentated formation of their mandibles, although they do not use them for the same purposes; this again exhibits an analogy of structure, that appears in the parasite to be merely corroborative of identity of existence.