l8(2 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 57 



The eyes are situated on each side just beyond the antennae (fig. 

 4). When pressed flat they show a crescentiform outline at the end 

 of a short strong peduncle. 



Appendages. — The antennae are long and slender with rather long 

 joints. Between the antennae 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 setae on their back margin. The posterior six pairs have all 

 the joints heavily fringed with setae 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 un- 

 doubtedly natatory in their action, and the basipodite also probably 

 carried branchiae 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. 



Sub-Class MALACOSTRACA 



Order HYMENOCARINA Clarke 



Family HYMENOCARID^ Salter 



Genus HYMENOCARIS Salter 



Hymenocaris Salter, 1853, Rept. British Assoc. Adv. Sci. for 1852. On the 

 Lowest Fossiliferous Beds of North Wales, p. 58. (Genus briefly de- 

 scribed. Genotype = Hymenocaris vermicauda Salter.) 



