Page:Walcott Cambrian Geology and Paleontology II.djvu/50

 are attached on the anterior side long spines carrying numerous smaller spines on the margin opposed to the main body of the appendage (pl. 4, fig. 4). There is also in this specimen a broad appendage of three joints attached to the outer posterior end of the basal joint. The features described are partially illustrated on pl. 4, by figs. 1-4. Fig. 3 illustrates some of the long spines where they are sufficiently separated to show the shorter secondary spines. Another unusual variation is illustrated by fig. 1. In the small specimen illustrated by fig. 2, pl. 2, it looks as though there were two jointed branches extending outward with small spines on their anterior margins. A larger series of specimens will undoubtedly enable us to interpret these chelate appendages more accurately but with our present information it seems probable that in the complex form represented by fig. 1, pl. 4, provision was made for capturing the numerous small phyllopod crustaceans and numerous annelids with which the bottom and adjacent water were abundantly supplied. It may be that the chelate, complex appendages were also used in fighting and that there was a marked difference in those belonging to the male and female.

The fourth pair of appendages so far as known have a small basal joint or gnathobase which has on its inner margin two strong spines, the form and size as compared with the gnathobases on the third and fifth pair of appendages is illustrated by fig. 1, pl. 5. The joints beyond the gnathobase are elongate and form a slender appendage that extends out beyond the third and fifth appendages. The terminal joint has three small spines projecting from its outer end.

Each of the fifth pair of appendages has a large basal joint or gnathobase, the inner margin of which is provided with short, strong spines. As far as can be determined from the material available for study, there are three or four strong, broad joints beyond the gnathobase, the outer of which are provided with fine setae or branchial filaments. The gnathobase is well shown by fig. 1, pl. 5, and the filaments on the outer joints by figs. 2 and 3, pl. 2.

Ventral appendages: Abdominal.—A number of specimens show more or less of traces of abdominal appendages on the first nine segments of the abdomen. None of these indicates the presence of a jointed appendage in any way comparable with the appendages of the cephalo-thorax, or the abdominal appendages of the trilobite. The appendages appear to be formed of clusters of branchial fringes attached to short lobes that are round or oval in outline and affixed to the ventral surface on each side of the abdomen at the outer