

106 The Ottawa Naturalist. [Dec. 



'"covering plates" are supported by small plates with a pit on 

 top, just as in Protop alee aster narrawayi. Outside the row of 

 plates bearing the "covering pieces" is a row of small spine- 

 bearing marginals, so that, though the plates are of very different 

 size, there is a complete analogy in arm structure between this 

 specimen and the one found by Mr. Narraway. If the specimen 

 had shown no more than this, it would have been a valuable 

 support to our interpretation of Mr. Narraway's specimen, but 

 on examining it more closely, small patches of top-shaped plates 

 were discovered. These patches are so arranged as to suggest 

 that they once formed part of a covering over the structures 

 now exposed on the arm. On comparing these plates with those 

 "on the abactinal side of Urasterella pulchella, (Billings), it was 

 found that they were identical with them. Furthermore, the 

 arms of the specimen are of the same shape as those of the 

 Urasterella, and that species has small, spine-bearing marginals. 

 The specimen figured is from the Walcott-Rust quarry at 

 Trenton Falls, N.Y., and is associated with specimens cf 

 Urasterella pulchella. 



This specimen shows that, in this case at least, the covering 

 pieces are really ambulacral ossicles, exposed by the removal 

 of most of the abactinal skeleton. Dr. H. L. Clark, to whom I 

 am indebted for many helpful suggestions in regard to this 

 matter, remarks that such a condition of preservation might be 

 expected to be very common, as the actinal side of a starfish, 

 being buried in the mud, might easilv be preserved, even though 

 the abactinal side, not so protected, disintegrated. 



The chief reason that Narraway, Hudson and myself had 

 for thinking that Protopalaaster narrawayi was exposed from 

 the actinal side was that the covering pieces did not look like 

 ambulacral plates, and that they made an apparently tight and 

 imperforate roof over the groove. These plates, instead of being 

 narrow and grooved at the sides for the protrusion of the tube- 

 feet, were wide, thin, and fitted closely together at the sides 

 and ends. But the same condition obtains in the specimen here 

 illustrated, and our argument must fall. A fact in regard to 

 Mr. Narraway's specimen to which we did not attach enough 

 importance is the way in which the marginal plates are truncated 

 on the side now exposed to view. The outer faces are rounded 

 and granulated, and one would expect the lower (actinal) faces 

 to be rounded also. The faces actuallv presented, however, are 

 flat and smooth, as would be expected if they served as a founda- 

 tion for the plates of the abactinal side. 



The specimen of Protopalaastcr also shows two plates 

 resting on the disk for which a place can not be found in the 

 structure of the specimen. (See figure 2 of the plate). Professor 



