216 Timehri. 
Megacanthopus, Ducke. 
This genus was formed by Ducke for some species formerly included in 
Polybia and a number of new ones. The species I have referred to it are much 
larger than the average Polybie and most of them have the abdominal petiole 
longer. Polybia basimacula, Cam. which is considered to be a var. of M. 
indeterminabilis, Saus. (A species not very satisfactorily described by 
Dubuyssom (Zool. Jahr ; 1910, 238 as is also M. Alfkeni, Ducke, l.c.) is cer- 
tainly a very different looking and much smaller species, being yellow with 
black markings and almost hyaline wings. The species I have described, as 
also one from Costa Rica, are all large, uniformly black and, with one excep- 
tion, have the wings uniformly fuscous violaceous. 
1. (2)—Base of thorax transverse, the sides projecting into a distinct, rounded angle, 
the abdominel petoile not much longer than the post-scutellum and metanotum 
united ; -the apical half widened ; the wings largely yetlowish hyaline. . . - 
ruficor nts. 
2. (1)—Base of thorax not angularly projecting laterally, the abdominal petiole longer 
than the scutellums and metanotum, slender, not widened at the apex, the wings 
fuscous violaceous. 
3- (4)—Base of thorax transverse, the scutellums, metathorax and legs rufotestaceous 
(abdominal petiole shorter than the thorax) . . . . . - . atriceps. 
4. (8)—Abdominal petoile as long or longer than the thorax. 
5. (6)—Dark testaceous, the stigma and alar nervures teStaceous—(the petiole as long as 
the; thorax; folk oe rotundicollis. 
6. (5)—Black, the stigma and nervures black. 
7. (8)—Abdominal petiole longer then the thorax ; the metanotal furrow rounded, not 
narrowed to a point at the top, not beginning at the base of metanotum . . 
longipetiolatus. 
8. (7) Abdominal petiole as long as the thorax, metanotal furrow narrowed to a point 
above, beginnng at the base of metanotal . . ... . violaceipennis. 
Megacanthopus rotundicollis, sp.n. 
Dark ferruginous, the lower part of the pleure lighter coloured, the abdo- 
men, cox, trochanters and femora of a lighter ferruginous colour, the tibie 
and tarsi fuscous, almost black ; wings fuscous violaceous, the costa and stig- 
ma ferruginous, the nervures black. Petiole as long as the thorax, and if 
anything, longer than the rest of the abdomen united, of almost equal width 
throughout, hardly thicker at the apex than at the base. Antennal flagellum 
black, the basal 6 or 7 joints of the flagellum black, dull rufous, below the 
ap‘cal points bright rufous. Base of pronotum above broadly rounded, the 
sides rounded, not angled. Male. Length 23 mm. 
Smooth, shining, the head and thorax densely covered with a white pile. 
Furrow in centre of metanotum commencing at the apex of basal fourth, nar- 
row at the base, becoming gradually wider and deeper towards the apex. 
Eyes distinctly converging below, reaching close to the base of the mandibles, 
the malar space hardly the length of the 2nd joint of the antennw. Clypeus 
longer than wide—about one-fourth the apex gradually narrowed to a bluntly 
rounded point and fringed with fulvous hair. The ocellar region and centre 
of front are blackish. The basal abscissa of radius is shorter than the follow- 
ing 2 united, the 2nd about one half the length of the 3rd ; the 2nd recurrent 
nervure is broadly roundly curved outwardly from top to bottom. 
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