THE THREE SPECIES OF THE GENUS ZILLA

We have three species of Zilla, the females of which are so much alike that it is almost impossible to tell them apart. The males also resemble each other closely except in their palpi, which are distinctly different in the different species. They are of moderate size, the largest about three-eighths of an inch long, and in general appearance resemble the genus Steatoda of the Therididæ (p. [119]). The abdomen is large and oval and a little flattened. The legs are slender and of moderate length, like those of Epeira. The head is rounded in front, and the lateral eyes are not separated farther from the middle pairs than they are from each other. The mandibles are large and thickened in the middle toward the front. The epigynum and the spinnerets are both small. The color of all the species is gray, with sometimes a little yellow or pink in the lighter parts. The cephalothorax has usually, but not always, a dark border at the sides and a middle dark line that widens and becomes lighter toward the eyes. The abdomen has a wide middle stripe like Epeira, scalloped at the sides and crossed at the hinder end by two or three pairs of transverse spots. In front it is almost white or tinted with pink or yellow, and narrows almost to a point, with a much darker spot each side. The sides of the abdomen are marked with oblique dark marks that extend underneath. The sternum has a light middle stripe. Under the abdomen is a dark middle stripe, with light each side of it. The legs are pale, with narrow gray rings at the end and middle of each joint. These three species seem to be the same as three found in Europe,—Z. atrica, Z. x-notata, and Z. montana. Atrica is found at Ipswich and Salem on the coast of Massachusetts, x-notata at Woods Hole on the south coast of Massachusetts, and montana in the White Mountains and Adirondacks. Wherever found they are in large numbers, atrica and x-notata living on the outside of houses, and montana in trees and rocks. The webs of Zilla [(fig. 432)] have a segment left without cross threads, sometimes for its whole length, and sometimes only the part of it nearest the center. Opposite this open segment a thread leads from the center of the web to the nest [(fig. 433)], which is a tube of silk open at both ends.

The differences between the palpi of the males are very plain. In atrica the palpi [(fig. 434)] are as long as the whole body, with the femur and tibia both slightly curved and the tarsus and palpal organ small and like that of x-notata. In x-notata [(fig. 435)] the palpus is as long as the cephalothorax, and the tarsus and palpal organ small and round. The front legs are a fourth longer than in atrica. In montana [(fig. 435a)] the palpus is still shorter, the tibia thicker, and the tarsus and palpal organ larger. There is little difference in the shape of the epigynum of the different species, but that of montana is twice as large as that of x-notata or atrica.

Singa pratensis.—The Singas are small Epeiridæ a sixth or fifth of an inch long, with smooth bodies and bright colors. They live among grass and other small plants in low open ground. When full grown the females of S. pratensis are a fifth of an inch long, with the abdomen oval and marked with a double white stripe in the middle and a single one on each side. The cephalothorax is yellow, with a little black between the middle eyes not extending to the lateral pairs. The legs are yellow, without rings or other markings. The abdomen is yellow brown, darker toward the hinder end, with white or light yellow stripes. The under side is the same yellow-brown color, darker in the middle, with two narrow, curved, light lines from the spiracles to the spinnerets. The males are marked in the same way and have a smaller abdomen and longer spines on the legs.

Singa variabilis.—This is a little smaller than pratensis, usually about a sixth of an inch long. The legs and cephalothorax are bright orange color. The front of the head between the eyes is black. The abdomen is usually entirely black, but occasionally has bright yellow markings [(fig. 436)] arranged somewhat as in pratensis. Sometimes there is a wide middle stripe, with narrower ones at the sides and two underneath. Sometimes there are only the two lateral stripes, and there are all variations between these markings. The males are colored in the same way and have the same varieties. They are smaller than the males of pratensis, but have the palpal organs as large or larger.