REVISION OF PALEOZOIC STELLEROIDEA. 179 



there are two specimens in the New York State Museum and six 

 in the Museum of Comparative Zoology, Harvard University, col- 

 lected by Dr. C. D. Walcott (Nos. 31-36). The American Museum 

 of Natural History has one specimen from Canajoharie, New York 

 (No. 660) ; in the Hall collection, Albany, there is a specimen from 

 Middle viUe, New York. At Hull, Canada, Mr. W. R. Billings col- 

 lected two specimens; the type and another specimen were found 

 by E. Billings at Ottawa, Canada; these are now in the Museum of 

 the Geological Survey of Canada at Ottawa. 



Remarks. This graceful species has the essential structure of 

 U. grandis and will therefore not require a detailed description. 

 U. pulchella is from a lower geological horizon, is probably the an- 

 cestor of U. grandis and has far less numerous abactinal plates, 

 which on the disk reveal a primitive arrangement reminding one of 

 Hudsonaster. In the center of the disk there is a single plate around 

 which is a first ring of 5 basal radial plates followed by another with 

 15 plates. The plates of the second ring are a little more conspicu- 

 ous than any other abactinal plates and are disposed as follows: 

 Five are radial in position and are the second basal plates of the 

 5 radial columns, while the other 10 are disposed interradially in 

 pairs immediately on each side of the second basal radials. The 

 plates interradial in position are the basals of the supramarginal 

 columns. Between the central ossicle and first ring there appear 

 to be a few small accessory plates. 



The arrangement of the disk pieces above described is plainly 

 preserved in a very young example (No. 36, MILS. Comp. Zool.). 

 The radial columns remain the most prominent while the supra- 

 marginals a little distally from the base of the rays are not readily 

 distinguishable from the other columns. Here and there an accessory 

 piece may be inserted between the radials and supramarginals but 

 the greater width of the rays is attained by increasing the size of 

 these columns and by the introduction of ambital columns outside 

 of the supramarginals. In a mature ray on each side of the radials 

 proximally, there appear to be not more than four columns of plates 

 but it is possible that a few pieces of a fifth column may be developed. 

 The form and spinosity of the abactinal plates is as in U. grandis, 

 except that the nonarticulating spines are less long in U. pulchella. 



Inframarginal columns at first view do not appear to be present 

 but a careful examination near the distal end of a ray reveals two 

 columns of nearly equal-sized plates on each side of the ambulacral 

 furrow. Here these plates closely adjoin, the adambulacrals are 

 elongate subquadrangular and the inframarginals quadrangular in 

 shape. Proceeding proximally the former become more prominent 

 and wider but remain throughout closely adjoining. The inframar- 

 ginals, however, gradually pass over to the abactinal side although 



