380 PROCEEDINGS OF THE ACADEMY OF [1890. 



and in the Fistiilata generally, the plate alluded to is succeeded by 

 a vertical row of plates in the tube, and that the anal plate (X), 

 where it exists, is followed by another row of plates, arranged in the 

 same way, and placed aside of the first row. Moreover, how can 

 that plate on the separation of the radials sink to the bottom of the 

 dorsal cup, when the anterior side of the tube rests upon the ventral 

 disk ? It would be practically impossible unless this side was low- 

 ered also. Is not the evolution that here took place more reason- 

 ably explained if we assume that on the separation of the radials 

 the space between them was filled by an additional plate ? 



We hold that the Fistulata have but one true anal plate — the 

 plate X — and that the radianal is a sort of supplementary radial, 

 which in some genera performed the functions of an anal plate. 

 The anal plate of the Camerata, when present, as before stated, in- 

 variably occupies the middle line of the posterior area, so as to sep- 

 arate the interbrachial plates into two equal divisions, even split- 

 ting the plates in rows in which there is an uneven number. Under 

 such circumstances it seems unreasonable to assume that the plate 

 X is a brachial, and the anal tube a modified arm. This suggestion 

 was made at first by us, but given up in 1883, finding it not sus- 

 tained by the phylogeny of the group. If it was a modified arm, the 

 arm structure should be indicated in Hybocrinus, one of the earliest 

 known Crinoids ; but, unfortunately for Bather's theory, the ventral 

 sac in this genus consists of only a small protuberance, composed of 

 irregularly arranged pieces. Nor do we find anything among Cys- 

 tids to support this hypothesis, and certainly not among Blastoids. 

 The theory is based wholly on a superficial resemblance between the 

 tube and arm-plntes in locriniis, and a misconception of the right 

 posterior radial which Bather took to be an axillary plate. But 

 even this apparent resemblance fades away on examining the tube 

 with the arms removed and the outer wings of the tube visible. 



Bather made no comparison with the anal i)lates of the Camerata. 

 He obviously regarded them as morphologically distinct from those 

 of the Fistulata, for on p. 319 he says : " it may be pointed out that, 

 as interradials do not enter into the composition of the dorsal cup 

 in any Fistulata, none of these plates can well be homologues of in- 

 terradials : in many of the Camerata actual interradials are present 

 in the anal area, but in the Fistulata at least we must look else- 



