Page:Walcott Cambrian Geology and Paleontology II.djvu/181

NO. 5 The posterior section is a little more than one-third the entire length of the animal. Posteriorly it grows smaller and terminates in a rounded end.

Surface.—The surface of the anterior and central sections is marked by numerous distinct, annular, impressed lines that divide it into many segments or metameres. In a specimen 26 cm. in length the annular lines average two to the millimeter along the anterior half of the body (fig. 3), while the posterior half is apparently smooth (fig. 5). Numerous fine setæ occur on the posterior end of the body. The smooth surface may be due to the condition of preservation, as some specimens of the anterior half show no traces of annular rings or segmens. From the mouth backward for a distance equal to four or five times the diameter of the flattened body the surface is thickly studded with elongated papillæ, as shown on the left side of figure 1. The papillæ appear to be arranged in longitudinal rows.

Parapodia.—Small, branching parapodia fringe the side of the body on several specimens (figures 4 and 5). There appear to be two, three, or even more divisions of some of the podia.

Proboscis.—A single specimen shows the proboscis protruded (fig. 1). It is slender and expanded toward the outer end where the surface is covered with numerous fine papillæ. The posterior half has many fine setæ extending obliquely forward. In fig. 3 the proboscis appears to have been retracted within the body and more or less crowded in on itself.

Mouth and anus.—The mouth is circular and surrounded by rows of strong setæ (figs. 1 and 3). No teeth have been seen. The anus is probably terminal as the enteric canal may be traced to within a very short distance of the posterior end of the body.

Enteric canal.—This canal is a rather large, elongated tube that extends from the mouth to the anus. It appears to be straight with an expansion at about the anterior third (fig. 2) that is quite marked in several specimens. In some examples the canal appears to be constricted by annular lines that divide it into segments two to three times as long as the segments of the body. There is a suggestion in one specimen that the body cavity was divided into a series of chambers by delicate muscular bands, but to be conclusive such an interpretation should be substantiated by evidence from other specimens.

Observations.—This beautiful annelid was first recognized from the specimen illustrated on pl. 18, figs. 1, 2 and 5. It was found