264 BULLETIN 88, UNITED STATES NATIONAL MUSEUM. 



Philadelphia, page 169, under the name of Protaster gregarius, which 

 they redefined and illustrated in the Geological Survey of Illinois, 

 volume 5, page 509, under the name of Protaster ( ?) gregarius. They 

 had numerous specimens 'in the condition of casts and molds, in 

 a very fine, somewhat granular matrix, that did not show the details 

 of its structure very clearly/ but they said, 'It will probably be 

 found to be generically distinct from the Silurian typical forms of 

 Protaster, but we prefer to place it provisionally in that genus for the 

 present.' In the collection of Mr. Gurley there are several specimens 

 belonging to this species, and they show a few characters not ob- 

 served by Meek and Worthen, and demonstrate very clearly this 

 species does not belong to the genus Protaster; we therefore propose 

 to include this species in a new genus, Aganaster, and describe the 

 characters, so far as known, as follows: 



" General outline, a central circular disk with five long, narrow 

 rays ; the circular disk on the dorsal side is covered with small polygo- 

 nal plates which are not interrupted by the presence of the rays, 

 thus showing the disk had a depth greater than the depth of the 

 rays; rays very narrow and convex or half cylindrical, spine bearing, 

 gradually tapering, and from the dorsal side appear as if composed 

 of plates arranged exactly opposite each other; the ventral side shows 

 a rather deep central disk with marginal plates. There are 10 oral 

 plates in the central part of the disk." 



Genoholotype and only species. Protaster gregarius Meek and 

 Worthen. 



Remarks. Aganaster "has nothing to do with Protaster and is 

 clearly a member of the Streptophiurse. As far as its characters are 

 known to me it must be included among the Eoluidiidae. It differs 

 from the rest of this family by the presence of dorsal arm plates. 

 * * * Bohm has founded the genus OpJiiopege on the type species 

 of Aganaster." (Gregory.) 



AGANASTER GREGARIUS (Meek and Worthen). 



Protaster f gregarius MEEK and WORTHEN, Proc. Acad. Nat. Sci. Philadelphia, 

 vol. 21, 1869, p. 169; Geol. Surv. Illinois, vol. 5, 1873, p. 509, pi. 16, fig. 5. 



Alepidaster gregarius MEEK, Amer. Journ. Sci., ser. 3, vol. 4, 1872, p. 275 (gen. 

 ref. only). 



Aganaster gregarius MILLER and GURLEY, Sixteenth Rep. Geol. Surv. Indiana, 

 1891, p. 372, pi. 9, figs. 10, 11; authors' extracts, 1890, p. 57, pi. 9, figs. 10, 

 11. MILLER, N. Amer. Geol. Pal., 1st. App., 1892, p. 673, fig. 1208. 



Description of 1873. "The disk of this species is circular in out- 

 line, slightly convex above, and measures from 0.20 to 0.30 inch in 

 diameter. In most cases it looks as if merely covered by a smooth, 

 membranaceous integument. Some casts of its external surface, 

 however, seem to show traces of flat, nearly smooth, imbricating 

 scales above. The five arms are slender, flexible, and rather long 



