PACKARD.] PHYLLOPODS OF NORTH AMERICA. 353 



lobe forming? a long', up-curved, chitiuous, slender api^endag'e, extend- 

 ing, ATlien 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, birauious appendage 

 extending out in front, the brush more than half the length of the body, 

 and sending oft' branches anteriorly, which are provided with minute 

 spinules. 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 antennae 

 are remarkably long and broad, oar-like, acute at the tip. The egg-sac 

 is long, subcorneal, 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, tig. 4 br.). The 1st endite or lobe is much 

 shorter than in the. other genera, and with coarser, hair-like setge ; the 

 2d endit« is large, being from one-third to one-half the size of the 1st 

 endite; the sette are rather coarse; the 3d and 4th endites small as 

 usual, each with three or four setulose setae ; the 5th endite is broad 

 and large, bluntly and quiteregularly 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. 1'he abdomen consists of nine 

 segments, dilates into a remarkably largo, 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 setag, 

 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. 



Thamnocephalm platyurus Packard, Bull. U. S. Geol. and Geogr. Siirvey Territories, iii, 



No. 1, 175. April 9, 1879. 



Male. — Prontal shrub over half as long as the body, the two branches 

 subdividing into about seven subbranches, all directed forward. Pirst 

 antennae long and slender, extending to the 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, cliitinous, 

 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 



