REVTSIOX OF PALEOZOIC STELLEROIDEA. 135 



plates is a ring of very large, thick, tumid, variously shaped, radial 

 and interradial plates. Of the latter there may be one plate inside 

 of the basal supramarginals of adjoining columns, or this plate may 

 be divided, when the pieces appear as inwardly crowded supramar- 

 ginals. Laterally and distally upon the interradials are situated the 

 large basal radial plates. The rays are bounded laterally by columns 

 of large, thick, subquadrate, tubercular supramarginals terminated dis- 

 tally by single ocular plates. These plates appear to be common to 

 both the actinal and abactinal areas and must therefore be the united 

 infra- and supramarginal columns. Between the supramarginals dis- 

 tally appear single small isolated plates wliich proximally become 

 larger and continuous, forming an inconspicuous column of radial 

 ossicles. On each side of this column are inserted a number of appar- 

 ently irregularly arranged small accessory plates which are hke those 

 of the disk. All of the plates of the abactinal area are finely tuber- 

 culose, these points being for the attachment of very fine, short spines. 



Madreporite small, rounded, not very convex, very finely radially 

 striated and resting directly upon two basal supramarginal plates of 

 adjoining rays. 



Ocular plates small but distinct, one terminating each ray and rest- 

 ing against the distal marginal plates. 



Supra- and inframarginal plates large and conspicuous, apparently 

 firmly united and indistinguishable laterally as separate columns. 

 Abactinally the supramarginal plates are mder and overlie more or 

 less the adambulacrals. 



Adambulacrals smaller than the inframarginals but otherwise 

 resemble the latter. 



Ambulacral grooves narrow. Ambulacral plates alternating, about 

 as numerous as the adambulacrals, h- -shaped, mth the podial open- 

 ings between adjoining plates. 



All other actinal characters unknown. 



Genoholotype and only Tcnown species. — Palseaster crawfordsvillensis 

 Miller. From the Keokuk crinid beds near Crawfordsville, Indiana. 



Remarks. — Neopalxaster retains a very primitive abactinal plate 

 structure and calls to mind Hudsonaster, Palxaster, and typical 

 Mesopalseaster. It is distinguished from these early Paleozoic genera 

 by the complete consolidation of the supra- and inframarginal plates 

 into one column, and the presence of ocular plates. The inter- 

 brachial area is unknown in Neopalaeaster, but its abactinal structure 

 seems to indicate a single interbracliial plate in each area bounded 

 distally by two basal inframarginal plates. If this interpretation is 

 correct, then this character wiU further distinguish Neopalxaster from 

 Hudsonxister and Palxaster. 



