200 PROCEEDINGS OF THE NATIONAL MUSEUM Vou. 113 
this change in the structure of the host plants was the source of a great 
deal of the selective pressure which brought about the modifications of 
the rostrum, genitalia, and antennae of the subgenera as they evolved. 
If the last idea is correct, the oldest species groups of Pachyphanes, 
Pseudosmicronyz, and Desmoris should show the closest resemblance to 
subgenus Smicronyx. The branches of the evolutionary tree in dia- 
eram 1 on page 199 have been arranged in an attempt to show that 
relationship. 
The reasons for the present placement of a given species group are 
presented in the discussion following the description of that group. 
Genus Smicronyx Schoenherr, 1843 
Micronyx Schoenherr, Genera et species curculionidum . . ., vol. 3, p. 423, 1836 
(preoccupied by Micronyx Boisduval, 1835). Type species, by original desig- 
nation: Micronyx reichi Gyllenhal, 1836. 
Smicronyz Schoenherr, Genera et species curculionidum . . ., vol. 7, part 2, p. 313, 
1843. Type species (ipso facto): Micronyzx reichi Gyllenhal, 1836. 
Description: Small species, smallest about 1.5 mm. and largest 
about 5.0 mm. in length. Covered, to a varying extent, with scales, 
which vary in size, shape, and color from one species to another. 
A few curled, setiform scales usually present on prothorax and elytra. 
Antennal funicles 7-jointed, first segment always longer than second 
segment (figs. 31-33). Antennal club 3-segmented, individual segments 
being difficult to distinguish, and entire surface of club covered with 
short hairs (figs. 31-33). Rostrum separated from rest of head by a fine, 
but distinct, constriction (figs. 3, 5, 7,9). Outer faces of mandibles hav- 
ing an unusual lobed condition (figs. 44-46). Eyes coarsely faceted, 
transversely oval, widely separated dorsally on head, and separated 
below to a varying extent. Anterior margin of prothorax emarginate 
ventrally (figs. 2, 35-36) and postocular lobes distinct (figs. 3, 7, 12). 
Base of elytra wider than prothorax and humeri well developed (figs. 1, 
6, 8). Scutellum small, but distinctly visible in all species except a 
few species of subgenus Pachyphanes (figs. 1, 6, 8). 
Abdominal sterna unequal in length, third and fourth sterna 
much shorter than first, second, or fifth sterna (fig. 2). Forecoxae 
globular and contiguous, hind coxae transverse and widely separated 
(fig. 2). Femora unarmed and clavate (figs. 2,4,6). Tibiae all armed 
with a small hook or with a mucro at inner angle of their apices; fore 
and mid tibiae (and hind tibiae in some species) bear a row of stiff setae 
on inner side. First three segments of tarsus spongy pubescent be- 
neath, third segment broader and bilobed, fourth segment bearing two 
claws, which are connate to a varying extent (figs. 39-42). 
Male genitalia: Median lobe (or aedeagus) somewhat flattened 
dorso-ventrally, heavily sclerotized at sides and sometimes on the 
