260 PROCEEDINGS OF THE ACADEMY OP [1885. 



and proximals (his orals) was clearly shown, and was also noticed 

 by him in his letter. We were, therefore, somewhat surprised 

 when we found them ignored in his discussion, and observed his 

 statement that " the so-called apical dome plates rest directly 

 upon the upper edges of the articular faces." We regret this the 

 more, as we should like to know whether he regards them as calyx 

 or perisomic plates. In our opinion they cannot be perisomic, as 

 five of them have a strictly radial position. Nor do we believe 

 that the five radial openings which we at first thought we observed 

 along the upper angle of these plates, at their juncture with the 

 proximals, are ambulacral or arm openings, as Carpenter suggests. 

 We are inclined to take them for mere depressions along the 

 suture, as it is very improbable that the ambulacra in proceeding 

 to the arms passed over these plates. We regard the five radial 

 pieces as radial dome plates, and the alternate ones as interradials. 

 Carpenter also omits to state whether the " orals " in Symbatho- 

 crinus consist of live or six pieces. That there are more than 

 five is clearly seen in the specimen which he examined, although 

 the exact number could not be ascertained. Other specimens, 

 however, which we have since prepared (PI. 4, figs. 9, 10), prove 

 clearly that there are seven pieces. This is morphologically of 

 the utmost importance, as showing that the summit structure of 

 Symbathocrimis is altogether different from that of Haplocrinus 

 or Bhizocrinus, with which Carpenter identifies it, and it is more 

 like that of Platycrinus. We shall return to this when we take 

 up the oral plates. 



As a result of the foregoing observations, we draw the follow- 

 ing conclusions, viz.: — 



1. Interradials are represented in all groups of the Palaeocri- 

 noidea. They were early developed in the larva, attained at once 

 large proportions, and persisted through life or were resorbed on 

 approaching maturity. 



2. They extend invariably to the proximals, or even cover them 

 completeby. 



3. They are more extravagantly developed in the earlier 

 groups, not always in number, but by extending over compara- 

 tively larger space. 



4. In all groups in which the arms are free from the first 

 radials, they are represented by only five single plates, and these 

 are located ventrally. Groups with two or more radials have 



