^I. marina^ (Linnæus), ^I. irrorata^ (Edwards). This species is about one inch long, and is easily recognized by the abdomen, the first three segments of which are narrow and terminate in acute teeth, while the other three are fused into one with straight sides and ending in three teeth, of which the middle one is the longest. The first pair of abdominal feet are large, long, and plate-like, covering the other feet and whole under surface of the abdomen like an operculum. The head is nearly square, the eyes are small, and the antennæ have long peduncles. The articulations of the thoracic feet are fringed with hair. The color of this species varies: sometimes it is light or dark green, or brown with black spots; again [pg294] it is striped longitudinally with light color. Sometimes the stripes run transversely in bands or spots. It is found from New Jersey northward on rocky shores of bays and sounds, or in eel-grass on sandy shores. ^I. ochotensis.^ A species very similar to the preceding, but a little larger, found on the Pacific coast. ^I. metallica.^ This species is a little smaller than /I. marina/, and differs from it in having the end of the telson truncated, or straight, instead of dentate. The head is nearly square. The body is broadest in the middle of the thorax; the projecting epimera give a serrate appearance to the sides. The abdominal feet are inclosed in the operculum-like scales of the first pair of feet. Its color is bright blue or green, often with a metallic luster when seen in the water. It is found swimming free or floating in masses of seaweeds from Long Island northward and also on the Pacific coast. ^I. wosnesenskii.^ A common species on the California coast, about one inch long and dark in color. The abdominal segments are united and bluntly rounded, and each has a small median tooth. The abdominal feet are inclosed by the opercular feet. Eggs and young are carried in a pouch. GENUS ^Chiridotea^ [Illustration: /Chiridotea cæca./] ^C. cæca.^ This species burrows beneath the surface of the sand, raising it up into a little ridge, and makes a mound at the end of the burrow, where it may be found. These trails are common on the wet sand. It imitates the sand in color, and is about half an inch in length, with a broad thorax and narrow abdomen terminating in a point. It is found on the New England coast. ^C. entomon^ (Linnæus). This species of the northern Pacific coast is from one to three inches long. The head has the appearance of two lobes, the sides having two rounded ends. The body is broad, the abdomen narrowing to a pointed end. The last segments of the abdomen are united, and the abdominal feet are inclosed by the first pair, which extend over them like an operculum. The epimera are broad, with acute lateral angles. CLASS =MERISTOMES= ORDER =XIPHOSURA= GENUS ^Limulus^