Page:Walcott Cambrian Geology and Paleontology II.djvu/260

 wrinkled and distorted in the shale. Ten specimens show it pressed down sideways so as to give the outline of a bivalve carapace (figs. 3 and 4, pl. 30).

The thorax is slender and composed of 8 rather short segments that bear appendages.

The abdomen is composed of one segment that is about the size of the last thoracic segment; it is followed by a long, slender, many-jointed telson-like extension that tapers gradually to a very fine, thread-like extremity. An abdomen of one segment has a telson 21 mm. in length attached to a body 12 mm. long, and composed of over thirty segments.

Eyes.—The paired eyes are shown on three specimens. In one a slight convexity still remains and in all a minute, round, bright dot indicates the eye a short distance within the anterior margin of the carapace.

Labrum.—A narrow labrum is outlined in a number of specimens between what appear to be two branches of the alimentary canal. In figure 1, plate 27, the labrum is on the under side and only the broad anterior end (stomach) of the alimentary canal is shown. In figures 2 and 3, plate 27, the labrum lies over the stomach and causes it to appear forked. It is shown more definitely in other specimens.

Appendages.—Many specimens have two slender, short-jointed antennæ projecting out from in front of the carapace (fig. 2, pl. 27). Others show a second shorter, smaller pair that is nearer the median line and probably represents the antennules. Several specimens have two or three very slender jointed appendages projecting from beneath the carapace posterior to the antenna. A flattened specimen of the under side of the head shows the basal joints of the first five pairs of appendages (fig. 3, pl. 27). An antenna may be traced to the second joint. The third shows only an obscure inner joint; the fourth has two long slender joints (1 and 2) and the fifth two rather broad joints. (Traces of the cephalic appendages are shown by fig. 2, pl. 27.) Where what may be the terminal joints of the third to fifth appendages project beyond the carapace, they are very delicate, slender, and one at least ends in two fine filaments.

The first five pairs of appendages are in front of the large tubes (cl, fig. 1) coming in from each side.

The thoracic legs have at least seven joints, the last pointed and curved slightly with a delicate terminal spine or claw. The three inner joints are larger than the outer and have a flattened triangular expansion of the inner side that gives a nodelike appearance to the