PACKARD.] PHYLLOPODS OF NORTH AMERICA. 358 
lobe forming a long, up-curved, chitinous, slender appendage, extend- 
ing, when outstretched, to the first third of the body; the lower lobe 
fleshy and short, straight. A distinguishing and remarkable character 
is the frontal, interantennal, shrub-like, branched, biramous appendage 
extending out in front, the brush more than half the length of the body, 
and sending off branches anteriorly, which are provided with minute 
spindles. The male genitals united at base as usual; they are small 
and deeply cleft. 
female—The frontal shrub is replaced by a pair of long, slender ap- 
pendages, acute, lanceolate-ovate at the end, and contracted somewhat 
in the middle. Labrum rather long and large. The second antennez 
are remarkably long and broad, oar-like, acute at the tip. The egg-sae 
is long, subconical, rather thick and broad at the base, which is con- 
cealed by the leaf-like feet; it ends in two valves. 
In both sexes the body is unusually short and thick, though the head 
is of the usual size. There are 11 pairs of feet, with the lobes broad and 
short, much more orbicular than usual. The gill is larger and broader 
than usual, the flabellum being somewhat ovate in outline (the relation 
of the gill to the rest of the appendage is best seen in the transverse 
view of the body, Plate XIV, fig. 4br.). The 1st endite or lobe is much 
Shorter than in the other genera, and with coarser, hair-like sete; the 
2d endite is large, being from one-third to one-half the size of the 1st 
endite; the set are rather coarse; the 3d and 4th endites small as 
usual, each with three or four setulose sets; the 5th endite is broad 
and large, bluntly and quite regularly pointed, not so rectangularly bent 
as in most of the other genera of the family. The 6th endite is usually 
short and broad, quite different from the long subacute-ovate form pre- 
vailing in the other genera of the family. The abdomen consists of nine 
segments, dilates intoa remarkably large, broad, fin-like expansion, be- 
ginning at the sixth segment from the end, and expanding at the last 
segment until it becomes wider than the body, and extending a little 
way beyond the last segment. It is fringed with delicate hair like sete, 
and canals from the body ramify in it; at the end it is deeply notched, 
forming two br. ad, rounded lobes. 
This remarkable genus differs from any other known to me by the 
short and broad, spatulate, fin-like expansion of the abdomen, while the 
male claspers are curved and simple. In both sexes the body is stout, 
broad, and the egg-sac of the female is subconical, spreading out at the 
base. It is quite unlike any European genus, and in the frontal append- 
age, the end of the abdomen, and the broad, short gills and endites 
stands alone in the family. 
THAMNOCEPHALUS PLATYURUS Packard. 
Plate XIV, figs. 1-7. 
Thamnocephalus platyurus Packard, Bull. U. 8. Geol. and Geogr. Survey Territories, iii, 
No. 1,175. April 9, 1879. 
Male.—Frontal shrub over halfas long as the body, the two branches 
subdividing into about seven subbranches, all directed forward. Virst 
antenne long and slender, extending tothe end of the basal joint of the 
second or male claspers. The latter with the basal joint rather short, 
the claspers long, slender, and recurved, simple, saber-like, chitinous, 
the lower lobe soft, acute, subconical. Genital appendages in the usual 
position, short, not so long as the segment to which they are attached, 
23 H 
