.. . 
182 
THERIDI1DZE. 
Theridion riparium. PI. XIII, fig. 115. 
Tkeridion riparium., Blaclcw., Research, in Zool., p. 354. 
— — Blackw., Annals and Mag. of Nat. Hist., second series, vol. viii, 
p. 338. 
— saxatile, Walck., Hist. Nat. des Insect. Apt., tom. ii, p. 328. 
Theridium — Koch, Uebers. des Arachn. Syst., erstes Heft, p. 8. 
— — Koch, Die Arachn., Band iv, p. 116, tab. 141, figs. 324, 325. 
Length of the female, 1th of an inch; length of the cephalo-thorax, nth, breadth, -th; 
breadth of the abdomen, T ' g th; length of an anterior leg, igtlis; length of a leg of the third 
pair, ^ths. 
In form and colour this species bears a close resemblance to Theridion Sisyphum, but may 
be distinguished from it by its smaller size and different economy. The cephalo-thorax is 
convex, glossy, slightly compressed before, rounded on the sides, and has a large indentation 
in the medial line; the falces are small, conical, and vertical; the maxillae are inclined towards 
the lip, which is quadrate ; the sternum is heart-shaped, and the palpi are short and robust. 
These parts are of a red-brown hue, the cephalo-thorax and sternum being much the darkest. 
The legs are moderately long and of a yellowish-brown colour, with broad, red-brown annuli. 
The four intermediate eyes form a square, the two anterior ones being seated on a protu¬ 
berance ; those constituting each lateral pair are placed obliquely on a small tubercle, and are 
contiguous. The abdomen is thinly clothed with hairs, pointed at the spinners, very convex 
above, and projects over the base of the cephalo-thorax; the upper part is of a red-brown 
colour, mottled with black and white, and bisected by an irregular, transverse, white line, 
interrupted in the middle by a triangular black spot, between which and the spinners there is 
a curved, transverse, black line; the under part, which has a brownish-black tint, is marked 
with a transverse band of red-brown near the spinners; and the colour of the branchial 
opercula is red-brown. 
The male is much smaller, darker coloured, and less distinctly marked than the female, 
but the relative length of its legs is the same. The cubital and radial joints of its palpi are 
short; the digital joint is somewhat oval, with a pointed process at its base, which falls into 
a notch in the radial joint and extends to its articulation with the cubital joint; it is convex 
and hairy externally, concave within, comprising the palpal organs, which are highly deve¬ 
loped, not very complicated in structure, and are of a red-brown colour. The convex sides of 
the digital joints are directed towards each other. 
The economy of this species, which is evidently identical with the Theridium saxatile of 
M. Koch, is very remarkable. It spins under the projections of broken, precipitous banks in 
the woods about Oakland a snare composed of fine, glossy lines, arranged after the manner of 
the Theridia. The union of the sexes takes place in July, and in August the female fabricates 
a slender, conical tube of silk, of a very slight texture, measuring from one and a half to two 
and a half inches in length, and about half an inch in diameter at its lower extremity; it is 
