94 PROCEEDINGS OF THE ACADEMY OF [1887. 



nosis, as stated by Etlieridge and Carpenter he says the summit is 

 "occupied by five or more small plates." In the diagram, on page 

 153 of the work cited, the summit is rej^resented as divided into five 

 equal and similar areas by the meeting of lines prolonged from the 

 middle of the ambulacra. It is apparent that no attempt was made 

 to give the exact form or number of those plates. They are not let- 

 tered as the other plates are, and no mention is made of them in the 

 explanation of the figure ; nor does Hall anywhere seem to have at- 

 tached sufiicient importance to the summit plates to give a descrip- 

 tion of their shape, position, arrangement, or relative size. 



In order to satisfy ourselves as to what the real facts are, Ave aj)- 

 plied to Prof. R. P. Whitfield for the loan of the type specimen of 

 E. elegans showing the summit plates, now in the collection of the 

 American Museum of Natural History in New York City. Prof. 

 Whitfield, with his usual kindness, for which we are under renewed 

 obligations to him, promptly sent us the original specimen from 

 which fig. 14, of PI. I, as well as the diagram on page 153 of the 

 15th Report was made; and in his letter transmitting it he says: 

 "I fear you will not see clearly the arrangement of the plates- 

 There are more than five jilates probably eight". The italics are his. 

 By applying water, colored with aniline, and then moderately brush- 

 ing the surface so as to remove the coloring matter excejit from the 

 sutures, we were enabled to distinguish the presence of a central piece 

 surrounded by seven others, four large and uniform, and three 

 smaller ones at the posterior side (fig. 11.) This gives a summit 

 structure substantially the same as that of Elaeacrlnus Verneuili, 

 (see Etheridge and Carpenter, Blast. Cat. p. 215). 



We also applied to Dr. Barris for the loan of his specimens of 

 Elaeacrinm obovatus, and these, together with our own, gave us 

 eight specimens of this species, all having the summit in situ. The 

 four large proximals are readily recognized in most of them, but 

 only a single specimen enabled us to distinguish all the plates as 

 they are shown in fig. 12. In four others, the suture line between 

 the central plate and the small anal piece is seen as plainly as we 

 could wish, but there is no trace of a suture toward the smaller 

 proximals (fig. 18); while in the three remaining ones, including the 

 largest specimen, it appears as if the summit consisted of only five 

 plates (fig. 14.) There is, however, no variation in the form and 

 general outline ot the summit in any of these specimens. The sum- 

 mit in all of them rests posteriorly between the two halves of the 



