Page:Smithsonian Miscellaneous Collections, Volume 85.djvu/110

Rh Functions of appendages.—The functions of the cephalic and thoracic limbs were probably similar to the functions of those of Marrella splendens.

Mode of occurence.—This delicate and beautiful little crustacean occurs abundantly in association with Marrella splendens and Waptia fieldensis, and is quickly recognized, even when distorted and crushed, by its carapace and strongly marked hepatic caeca. The carapace is almost always outlined on the shale, as are frequently the body and telson; the large strong endopodites are usually more or less clearly marked, although their jointed structure has generally been lost in the flattening in the shale; the exopodites were so delicate that they are rarely preserved, and the same is true of the labrum and eyes.

Comparison with crustaceans.—Burgessia has certain characters in common with Marrella and Naraoia and belongs in a group with them which will be discussed later (p. 37).

Diagrammatic restorations of ventral surface.—I have endeavored to present, in text figures 3, 4, and 5, interpretations of the structure of my Burgessia bella.

Plesiotypes.—U. S. N. M., Nos. 83947a-o.


 * Waptia fieldensis Walcott, 1912, Smithsonian Misc. Coll., vol. 57, no. 6, 1912, p. 181, pl. 27, figs. 4, 5.

The general characters of this species were described in 1912, since when a large number of specimens have been collected from the Burgess shale, a few affording data from which a fairly accurate diagrammatic restoration of the animal may be drawn (text fig. 6).

Exoskeleton.—The exoskeleton of the carapace, trunk, and caudal furca was very thin and readily distorted. The trunk consists of 5 to 7 short cephalic segments; 8 narrow thoracic segments, each bearing a pair of uniramous appendages; 6 long abdominal segments and 2 broad lobelike terminal caudal furca or rami; the latter have three transverse lines indicating four fused segments. The posterior margin of the abdominal segments bears four or more strong spines with a fringe of small, short, sharp spines between them. The last or anal segment has a minute anal opening on a slightly rounded elevation near its posterior ventral margin. The abdominal segments have often been narrowed and lengthened, or broadened and shortened by distortion in the shale.