NO. 6 NEW AMERICAN EDRIOASTEROIDEA BASSLER 3 



the under surface possibly by larger polygonal ones similar to the 

 interambulacrals. 



Good examples of this interesting species would undoubtedly re- 

 veal a beautiful and remarkable structure for this early edrioasteroid. 

 The large proportions, strongly curved ambulacra, and numerous 

 large polygonal interambulacral plates readily distinguish it from 

 the associated genotype. 



Occurrence. — Middle Cambrian (Burgess shale), Burgess Pass, 

 above Field, British Columbia (loc. 35k). 



Holotype. — U.S.N.M. no. 90755. 



STROMATOCYSTITES Pompeckj, 1896 



In this genus the under surface of the theca is completely occupied 

 by more or less regular polygonal plates, a feature so different from 

 most other edrioasteroids that further studies of well-preserved 

 material are much needed. Figures of the upper and lower surfaces 

 of the genotype, 6". pentangularis Pompeckj, from the Middle Cam- 

 brian of Bohemia, are reproduced on plate i, figures 6, 7. 



XENOCYSTITES, n. gen. 



Theca a circular, depressed, hemispherical sack with the oral sur- 

 face (although not directly observed) bearing five narrow, slightly 

 curving ambulacra undoubtedly separated by many polygonal mosaic 

 interambulacral plates (possibly eight rows -at the periphery), and 

 the basal side made up of similar, polygonal plates either completely 

 covering this area or possibly leaving a small central opening mark- 

 ing the point of attachment. Anal area not observed. Basal covering 

 plates of ambulacra long, narrow, in a single row. 



Genotype and only known species. — X. carteri, new species. 

 Chemung of New York. 



XENOCYSTITES CARTERI, n. sp. 



Plate 7, fig. 14 



This interesting species is based upon a flattened circular disk, 

 45 mm in diameter, exposing the basal side of half of the theca which 

 is covered with polygonal plates but shows the ambulacra clearly 

 impressed upon these basal plates. Weathering exposing the under 

 side of the plates of the oral surface indicates that they too are 

 polygonal and mosaic and that the ambulacra have long, narrow basal 

 floor plates in a single row. The central part of the base consists of a 



