Page:Walcott Cambrian Geology and Paleontology II.djvu/264

 The eyes are situated on each side just beyond the antennæ (fig. 4). When pressed flat they show a crescentiform outline at the end of a short strong peduncle.

Appendages.—The antennæ are long and slender with rather long joints. Between the antennæ in one specimen a pair of short lobe-like appendages occur that for the present I shall consider as the antennules. They are not shown in the specimens illustrated. The first pair of leg-like appendages seen show six joints to where they are lost beneath the carapace (m, fig. 5). The next posterior four have fine curved spines on the terminal joint with short joints carrying strong setæ on their back margin. The posterior six pairs have all the joints heavily fringed with setæ and the terminal joint apparently has two or more narrow, elongate, lobe-like prolongations. Pressed down on the basal joint there is a lance-shaped, short, flat lobe that may be the exopodite or possibly the epipodite. The large, broad, setiferous, outer joints of the six posterior pairs of legs were undoubtedly natatory in their action, and the basipodite also probably carried branchiæ on the epipodite. On one specimen such lobes are shown on three of the legs. No traces of any appendages have been seen on the posterior six segments of the body.

Alimentary canal.—This may be traced as a small, straight canal from the head back to the point where the caudal rami unite with the posterior segment.

Dimensions.—The largest specimen in the collection has a length of nearly 65 mm. Its proportions, in side view, are shown by figure 5, plate 27.

Observations.—This is one of the most beautiful and graceful of the remarkable group of crustaceans from the Burgess shale. It occurs in relative abundance but unfortunately I have not yet found a specimen showing clearly the arrangement of the various appendages beneath the anterior portion of the body.

Formation and locality.—Middle Cambrian: (35k) Burgess shale member of the Stephen formation, on the west slope of the ridge between Mount Field and Wapta Peak, one mile (1.6 km.) northeast of Burgess Pass, above Field, British Columbia.


 * Hymenocaris, 1853, Rept. British Assoc. Adv. Sci. for 1852. On the Lowest Fossiliferous Beds of North Wales, p. 58. (Genus briefly described. Genotype = Hymenocaris vermicauda Salter.)