I915.] EF. H. Gravety: Lucanidae of the Indian Museum. 409 
frons appears only as an exceedingly obscure transverse convexity 
about one-third of the way from the clypeolabral ridge to the ridge 
between the anterior angles of the head. That this obscure con- 
vexity does really mark the junction of the clypeus and the frons 
is confirmed by the fact that in Hexarthrius forsteri—a species of 
which the female is unknown to me—it is replaced by a very 
distinct suture.’ In Hexarthrius forstert the clypeolabral ridge is 
replaced by a pair of angular processes, structures which reappear 
in many species of Lucanidae, and may be supposed when present 
always to represent this ridge. 
The presence of these processes, or of the ridge from which they 
are derived, distinguishes the genera Eurytrachelus and Platypro- 
sopus from Hemtsodorcus and Dorcus. But when the whole ridge 
is present it is often very low, and there seems reason to think 
that it has sometimes been overlooked, with the result that species 
of Eurytrachelus have been placed in the genus Doycus, and that 
the differences between the prosterna of these two genera have 
come to be regarded as of no importance. 
The morphological anterior margin of the labrum is, how- 
ever, densely fringed with hair, and the clypeolabral ridge is hairless. 
When, therefore, the apparent anterior margin of the clypeolabrum 
as seen from above is hairy, and no ridge or processes are seen, 
the specimen will belong to the genus Hemzsodorcus or Dorcus. 
When, however, it is hairless, a closer examination will show 
that this margin is really the clypeolabral ridge and that the true 
anterior margin of the plate is hidden beneath it. 
The genera Hemisodorcus, Dorcus, Eurytrachelus and Platy- 
prosopus may then be distinguished thus :— 
Posterior end of prosternal process abruptly rounded 
or truncate in both sexes, its horizontal surface raised 
well above surface of mesosternum se Be tk 
Posterior end of prosternal process lower in both sexes, 
either uniformly depressed, or convex in front of a 
narrow depressed border defined on the inner side 
by a marginal groove 
_ 
. 
w 
Clypeolabral ridge absent in male; female with upper 
tooth of mandibles very strong and with a median 
cephalic tubercle .,, a os ... Hemisodorcus. 
Clypeolabral ridge present in male (often as a pair of 
lateral teeth) ; female with upper tooth of mandibles 
very weak and with a pair of cephalic tubercles ... Eurytrachelus. 
to 
Antennae normal in both sexes; clypeolabral ridge 
absent in male; female with a pair of cephalic 
tubercles hs ae see ~3.  LIOYCUS, 
3- ) Seventh joint of antenna (the last before the three bear- 
ing pilose lamellae) with a slender polished anterior 
process as long as the lamella of the succeeding joint 
and tipped with a cluster of hairs (? in both sexes) ; 
clypeolabral ridge present in male ; female ? .. Platyprosopus. 
___ |! This suture is also present in the other species of Hexarthrius in our collec- 
tion ; but in them the clypeus is disproportionally large, the labrum being reduced 
to a narrow strip along its outer margin. 
