Geometridae of the Argentine BepuUic. 235 
they agree in structure and general facies; but in both, 
the ferruginous areas are pale ocbreous, the basal patch 
somewhat more angulated, the inner edge of the median 
band more strongly concave, and the underside somewhat 
lighter and more sharply marked. The La Paz example 
is extreme in these respects and may be brietly diagnosed 
thus : 
ah. angidata, Prout (nov, ab.). 
Basal, median and terminal areas much darker, the median 
somewhat constricted, pale subterminal line moderately distinct, 
conspicuous at costa ; basal area and inner edge of median angled 
in cell; hindwing beneath with a strong dark central line separating 
the two areas. 
So far as I am aware, this species and those which 
follow are the first recorded representatives of the genus 
Lithostege in the Neotropical Region, and their discovery 
is vei’y interesting, I have much pleasure in dedicating 
the present pretty little species to my kind friend Dr. 
E. Giacomelli, from whom we may expect further valuable 
discoveries in the little-worked district of La Rioja, not¬ 
withstanding that he finds it but poor in species. 
57. Lithostege pax (Prout), nov. sp. (Plate XLVIII, 
fig. 30.) 
d $. 20-22 mm. Head and body fuscous grey ; thorax paler 
beneath. Forewing with costa and termen somewhat rounded, shape 
therefore intermediate between Lithostege and Chesias, which have 
not hitherto been very sharply defined ; basal area fuscous grey, 
bordered by a darker line, which is bent outwards; to this follows a 
paler area (in the type and some others much paler and sometimes 
more brownish tinted, in darker examples little paler and not tinged 
with brown), traversed by one or more dusky lines, which are angled 
in the cell ; median band fuscous grey, its proximal margin strongly 
inbent, its distal margin much as in L. giacomelUi; a dusky line 
traverses this band parallel to its distal margin; a pale, sometimes 
white line borders the median band distally ; outer area concolorous 
with that between basal and median bands, traversed by some in¬ 
distinct or moderately distinct wavy lines (vcxriable in individual 
specimens), sometimes with the distal margin a little darkened, 
sometimes with faint traces of an oblique streak from apex, or of the 
“ twin spot” so frequent in the Larentiinae, one with a conspicu¬ 
ous pale (browmish tinted) dash between SC^ and from end of 
