NO. 3 BURGESS SHALE FOSSILS WALCOTT 15 



NARAOIA SPINIFER, new species 

 Plate 15, fig. I 



Three specimens referred to this species are known, of which tlic 

 one figured shows best the spines on the margin of the posterior 

 dorsal shield ; another preserves both the carapace and dorsal shield, 

 the latter having marginal spines while the carapace has a smooth 

 margin. On the third specimen the test of the dorsal shield is nearly 

 all exfoliated on the left side so as to expose the body, several of the 

 fringed exopodites, and coming from beneath them the distal portions 

 of the endopodites. 



This species differs from Noraoia compacta in having eight short, 

 small spines on the outer margin of the dorsal shield equally spaced 

 between the anterior margin and a large posterior median spine ; all 

 three of the known specimens of the posterior dorsal shield are also 

 larger than those of A'', compacta, as they average 25 mm. in length 

 exclusive of the posterior median spine. The one specimen preserving 

 the carapace indicates that it was similar to the carapace of A^'. com- 

 pacta, the recognized differences between the two species being con- 

 fined to the posterior dorsal shield. 



Holotypc.—U. S. N. M., No. 83946., 



BURGESSIA Walcott 1912 



BURGESSIA BELLA Walcott 



Plate 15, figs. 4-7; plate 16; plate 17; plate 18, fig. i 



Biirucssia bclla Walcott, 1912, Smithsonian Misc. Coll., vol. 57. no. fi, p. 177, 

 pi. 27, figs. 1-3; pi. 30, figs. 3-4. 



Since the publication of the original description of Biirgcssia bclla 

 Walcott, a large number of more or less well preserved specimens 

 have l)ecu collected from the Burgess shale, a few of which preserve 

 details of structure that make it possible to draw a diagrammatic resto- 

 ration indicating the increase in our information of the cephalic and 

 thoracic appendages (text figs. 3, 4). 



Exoskclcton. — The exoskclcton is very delicate and the cara])ace 

 is so thin as to be almost meml)ranaceous. The segment to wliich the 

 telson is attached appears to l)c partly covered ventrally l)y a heart- 

 shaped plate that is attached to the anterior margin of the segment 

 or to the ])osterior ]iml)-l)cariiig segment of the tliorax; it suggests a 

 supra-anal plate. 



There apjx^ar to be five cephalic, eight thoracic, and one abdominal 

 segment, also a long, slender telson with numerous joints. One ex- 

 ample 21 mm. in lengtli has 30 joints. 

 2 



