1969] 
Brown and Kempf — Acanthognathus 
89 
even though its nests tend to be cryptically situated in the ground or 
rotten wood. Like most or all Orectognathus, the related Australian 
genus, its species probably forage mainly at night. 
Acanthognathus 
Acanthognathus Mayr, 1887:578. Type species Acanthognathus ocellatus, 
monobasic. 
Acanthognathus : Emery, 1922, Gen. Insect., 174c :3 17-3 18. — M. R. Smith, 
1944:150-152, key to spp. — Brown, 1948:125, in generic key. — Brown 
and Wilson, 1959:281-283, phylogeny, biology. 
Worker: Size small (TL 3. 5-4.6 mm). Habitus of strumigeni- 
form Dacetini, i.e., with head much longer than broad, more or less 
depressed dorsoventrally, and much narrowed and drawn out anteriad, 
with a deep posterior excision (Figs. 1, 11); mandibles greatly 
elongate, narrow and linear, straight or nearly so, each with 3 spini- 
form apical teeth. Somewhat beyond the midlength of each mandible, 
there is often a small welt or convexity on the inner margin, whence 
issues a long, fine hair, the trigger hair, which lies flat against the 
margin when the mandible is closed, but which stands erect when 
the mandible is open, pointing straight forward, and serving as a 
tactile range-finder. Preapical teeth or denticles also occur on the 
mandibles of some species. Near the base of each mandible a long, 
slender basal process arises from its ventral surface and runs obliquely 
basoventrad, crossing its opposite number when the mandibles are 
closed ( Fig. 1 ) ; the apices of these processes are split into a pair of 
short acute teeth, by means of which they engage one another when 
serving as props to hold the mandibles widely open. (The basal pro- 
cesses have also been observed by Moeller and ourselves to be used 
in carrying brood in rudis and ocellatus t with mandibles opened 
^videly.) 
Frontal lobes form small convex shields over the antennal inser- 
tions. Eyes large, near or slightly in front of middle of sides of 
head, only moderately convex, normally with 40 to 70 or more 
facets. Clypeus narrowly bell-shaped, flat, with long posterior lobe 
inserted between frontal lobes. Antennae long and slender, 11- 
segmented (Figs. 1,4,11), with the scapes oddly bent and usually 
constricted near apex. Small antennal segments III through IX in 
a rigid straight line, and may sometimes be fused internally, cor- 
responding (as Santschi has already pointed out) to the long segment 
III in the Australasian genus Orectognathus. Antennal scrobes 
lacking. Occipital area deeply and broadly concave, set off from 
vertex by a sharply rounded angle. 
