176 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 5/ 



carapace was very thin and is now frequently wrinkled and folded in 

 a manner resembling pressed and dried specimens of the carapace of 

 the recent Lepidurus glaciaUs. 



The two parts of the carapace appear to be attached along the longi- 

 tudinal median line to the dorsal surface of a number of the segments 

 of the head and thorax. The line between the two parts of the cara- 

 pace appears to be at about the third thoracic segment of the body. 

 There is nothing in the appearance of the cephalic carapace to indi- 

 cate how many segments are coalesced in it, but on one specimen of 

 a posterior part 14 segments are faintly indicated. Whether these 

 are only the impressions of the underlying segments or represent 

 coalesced segments I am not prepared to state. 



The body is slender and composed of several cephalic segments, 

 probably 5, and 17 to 19 thoracic segments. Three of the latter 

 appear beneath the anterior part of the carapace, 14 beneath the pos- 

 terior part, and two extend beyond the posterior edge of the carapace. 

 An abdomen is indicated by two small segments and a short, slender- 

 jointed telson-like extension (fig. 4). 



Appendages. — In the head of Burgessia hclla (pi. 27, fig. 3) the 

 cephalic appendages are all anterior to the lateral canals connecting 

 the hepatic cseca and alimentar)^ canal. Specimens of Naraoia com- 

 pacta show the hepatic tubes, and anterior to it .the outline of four 

 divisions or segments of the central axis of the head. What may be 

 the outer end of a simple straight antenna projects from the side of 

 the carapace, and seventeen legs extend from beneath the carapace 

 in figure 4. Of these, three are referred to that portion of the bodv 

 beneath the anterior part and 14 to the posterior part of the carapace. 

 The legs have long, slender joints, all of which except the distal have 

 a strong fringe of fine setse. The legs terminate in a minute, slightly 

 curved claw. I have not seen a flabellum or gill in position, but con- 

 siderable evidence of their presence along the side of the body is 

 furnished by faint outlines showing through the carapace. 



Interior structure. — The large hepatic caeca are beautifully shown in 

 the sides of the anterior half of the carapace (fig. 4) also the canal 

 connecting with the alimentary canal. The latter canal is finely 

 shown in the thorax, where it extends to the posterior segment a little 

 back of the posterior margin of the carapace, where the slender telson 

 joins the body. 



Observations. — This species furnishes another interesting addition 

 to the group of Middle Cambrian Branchiopoda from the Burgess 

 shale. It is essentially Burgessia-XWae (pi. 2y, figs. 1-3) with the ad- 



