DESCRIPTION OF GENERA AND SPECIES. 257 
Appomen; Subcylindrical, widest toward the base, rounded and somewhat narrow in 
front, where it overhangs the cephalothorax ; somewhat narrowed at the apex, which slightly 
overhangs the spinnerets; dorsum but little arched, yellow, with veined branching lines 
from the middle to apex and scalloped marginal lines; the surface thickly covered with 
short silvery hair, which gives the organ a metallic white color; the skin color is yellow. 
The epigynum (Plate XXII., Fig. la) shows simply a thickened flap, obtusely triangular, 
without a scapus, and set opposite a conical process upon the posterior side of the genital 
cleft, which is thus inclosed between two liplike elevations. 
Disrrreurion: Southern California. The habitat of this species is. somewhat in doubt. 
Dr. Marx received it from Professor Ulysses Brown, Edinburgh, Scotland, and it was con- 
tained in,a broken box, the label of which was mutilated; but in the same box were 
several bottles, labeled “Group of southern islands, Santa Barbara, California.” 
Genus THERIDIOSOMA, Camprinas, 1879. 
This genus forms a connecting link between the Orbweavers and Theridioid spiders. It 
was created by Cambridge for the kindred, and perhaps identical, species Th. gemmosum, 
and assigned to the Retitelarize, but was transferred by the writer to the Orbitelarize, both 
on accoant of its habits and structure.1 The individuals are very small, of delicate colors, 
and in general form resemble the species of Theridium. The cephalothorax is cordate, 
truncate at the base, the head much elevated, the face wide and projecting in front, the 
corselet grooves and cephalic suture are distinct, the skin glossy. The sternum is cordate 
or obtusely triangular; almost as wide as long, The labium is short, scarcely one-third the 
height of the maxillge, which are as wide as, or wider, than long, in the female. The 
eyes are divided into three groups, the central quad longer than wide, and the greatest 
width behind; the midrear eyes being much the larger, and placed close together, rela- 
tively much closer than the midfront. The space between the sidefront and midfront eyes 
is twice the intervening space of the latter, or about equal to the area thereof; the clypeus 
is high; the front row of eyes is aligned, or a very little recurved; the rear row decidedly 
procurved. The legs are 1, 2, 4, 3; rather stout; scantily pubescent; provided with sharp, 
bristlelike spines. The mandibles are long and conical. The abdomen is a rounded oyal, 
the dorsum high, arched to the distal spinnerets, and is carried by the spider in a nearly 
vertical position. The epigynum is a large yaulted atriolum, without a scapus, occupying 
half the width of the venter. The male resembles in. color and markings the female, 
though somewhat smaller in size. The palpal bulb is globular, and the accessory organs 
complex and much lengthened. This spider makes an orb web of the characteristic Epeiroid 
type, but captures its prey by means of a trapline, which it uses somewhat in oe fashion 
of Hyptiotes, by alternate rapid tightening and releasing. 
No. 105. Theridiosoma radiosum McCoox. Plate XXVII, Figs. 8, 9. 
1881. Lpeira radiosa, McCook . .. . Proceed. Acad, Nat. Sci., Phila., p. 163. 
1884. Microepeira radiosa, Emerron . . N. E. Ep., p. 320, pl. xxxiy., Fig. 7. 
1889. Theridiosoma gemmosum, McCoox, Amer. Spiders and their Spinningwork, Vol. I, 
ch, xii. 
1889, Theridiosoma radiosum, Marx. . Catalogue, p. 551. 
Fremate: Total length, 2.5 mm.; cephalothorax, 1 mm. long, 9 mm. wide; abdomen, 
1.5 mm. long, 1.3 mm. wide. These measurements vary somewhat according to the speci- 
mens, some being larger, some smaller. Count Keyserling, who had thoroughly studied and 
described Th. gemmosum Cambridge, also knew and described in manuscript the American 
* Volume I., chapter xii. 
