REVISION OF PALEOZOIC STELLEROIDEA. 85 



slender rays, with more angular spaces between. It also differs in 

 having but two ranges of plates on each side of the ambulacral 

 grooves, on the under side, instead of three. These pieces are about 

 of the same size in each row, and sometimes appear to alternate; 

 they are all rather prominent, and those of the outer range project 

 a little laterally in the form of small nodes. Toward the outer 

 extremities of the rays, however, the lateral ranges are contracted 

 behind the others, so as to be scarcely visible from below. About 23 

 of these pieces may be counted on each side of the ambulacral furrow 

 in each ray. The ambulacral furrows are very narrow, and indeed 

 seem to be closed toward the extremities of the rays, by the gradual 

 approximation of the inner rows of pieces on each side, which alter- 

 nate and appear to fit together. 



"Our specimen only shows the under side, but along the outer 

 margins of two of the rays, there is some appearance either of the 

 overlapping of some of the dorsal parts by pressure, or of a slightly 

 developed disk. This part does not seem to have any distinct range 

 of marginal plates, but appears to be made up of small pieces, covered 

 with granules, or bases of small spines. 



"We take pleasure in dedicating this interesting species to 

 Prof. C. D. Wilber, of the Illinois State Normal School, to whom we 

 are indebted for the use of the only specimen we have seen. 



"Greatest diameter about 1 inch; smaller diameter 0.33 inch. 



"Locality and position. Oswego, Kendall County, Illinois, in rocks 

 of the age of the Trenton or Hudson River Group of the New York 

 series." Probably equivalent to the Richmond beds of the highest 

 Ordovicic. The whereabouts of the type-specimen is not known. 



Remarks. Hall pointed out that this species is not a Petraster 

 because P. wilberanus has but two columns of plates on each side of 

 the ambulacral groove, while Petraster has in addition "a few disk 

 plates on the ventral side." He therefore referred it to Pal&aster. 

 However, Meek and Worthen describe the abactinal area as having 

 no " distinct range of marginal plates, but appears to be made up of 

 small pieces, covered with granules, or bases of small spines." The 

 characters as far as mentioned appear to be those of Mesopal&aster. 

 Should there prove to be in P. wilberanus single axillary interbrachial 

 plates, then all of the characters will be in harmony with Mesopalse- 

 aster and M. proavitus may prove to be a synonym of it. This 

 can not be proven at present since we have not been able to locate 

 the type-specimen. 



MESOPAL^ASTER (?) DUBITJS (Miller and Dyer). 



Palseaster dubius MILLER and DYER, Cont. to Pal., No. 2, 1878, p. 5, pi. 4, fig. 8. 



Original description. "Pentagonal; rays longer than the diameter 

 of the body, and uniformly tapering. The ambulacral groove is 

 sharply angular in the middle, formed by two series of plates having 



