NO. 6 NEW AMERICAN EDRIOASTEROIDEA BASSLER I 5 



HEMICYSTITES (?) CARBONARIUS, n. sp. 

 Plate 4, figs. 10, ii 



This curious edrioasteroid occurs as thin, parasitic disks, the largest 

 1 1 mm in diameter, attached to a smooth cephalopod shell. The amhu- 

 lacral areas although radiating straight from the center are obscured 

 as to their detailed structure. This radiate arrangement and the 

 aspect of the encircling rows of plates are so like Hemic ystites that 

 the species can be referred there at least provisionally. Young speci- 

 mens show even less definite arrangement of the ambulacral plates 

 than mature examples. 



Occurrence. — Pennsylvanian (Bluefield shale), railroad cut f mile 

 east of Adds Valley, West Virginia. 



Cotypes. — U.S.N.M. no. 91837. 



Family AGELACRINITIDAE Bassler, 1935 



Theca as in the Hemicystitidae except that the plates covering the 

 oral area are small, numerous, and without any definite order. A 

 single row of ambulacral flooring plates overlapping proximally. 



Agelacrinites Vanuxem, 1842, Isorophns Foerste, 1916, Isorophii- 

 sella Bassler, 1935, Thresherodiscus Foerste, 19 14, DiscocysHs 

 Gregory, 1897, Cooperidiscus Bassler, 1935, Ulrichidiscus Bassler, 

 1935, and Lepidodiscits Meek and Worthen, 1868, are placed in this 

 family as restricted, the arrangement of the oral covering and ambu- 

 lacral flooring plates being regarded as important characters. 



THRESHERODISCUS Foerste, 1914 



In this genus the branching of the ambulacral rays is carried to an 

 extreme as shown in the illustration of the oral side of T. ramosus 

 Foerste, the genotype and only species from the Lower Trenton of 

 Manitoulin Island, Lake Fluron (pi. 2, fig. 8). The illustration shows 

 also that the rays have a pronounced trimerous origin which is perhaps 

 the condition existing in many of the edrioasteroids. The interambu- 

 lacral plates are large and squamose, imbricating in the central part 

 and smaller along the border. 



AGELACRINITES Vanuxem, 1842 



This genus, fairly well represented in the Upper Paleozoic of both 

 America and Europe, is readily recognized by its five long, narrow, 

 much curved ambulacra, two of which (4 and 5) bend to the right, 

 and three (i, 2, 3) to the left, and by the sculptured, mosaic inter- 



