382 PROCEEDINGS OF THE ACADEMY OF [1890. 



higher level than the one to the left, and does not touch X, nor does 

 it touch the adjoining brachial, and is therefore a plate of the 

 tube ; while that to the left, which is laterally connected with the ad- 

 joining radial, actually forms a part of the dorsal cup. Both plates 

 rest by their lower faces upon the sloping upper sides of adjacent 

 radials, and each of them, as well as the middle plate — resting u})()n 

 the truncate upper face of X — supports a vertical row of plates in 

 the tube. These plates are not represented in Bather's diagram of 

 Dendrocrinus, but are shown by our figure. 



Now, if it is true that the plate which rests upon the left upi)er 

 sloping side of the compound radial, represents morphologically the 

 plate t in Poteriocrinus, and we think Bather will have to admit 

 this, what then is his plate X in locrinus and Merocrinusf This 

 plate, like t in Dendrocriinis, rests upon the left upper sloping face 

 of the compound radial. Like that it is a free plate of the ventral 

 tube, and like that it supports a vertical row of tube plates upon its 

 upper face. The only real difference between these plates in the two 

 genera is that the facet of the radial in Dendrocrinus is horse-shoe- 

 shaped, and that of locrinus straight. This structure was evidently 

 not understood by Bather, or he would never have called the radial 

 of locrinus an axillary plate. There would be just as much propriety 

 in calling the radials of an Actinocrinus axillary plates, for they 

 support in a similar manner upon their upper sloping faces the first 

 interbrachials. 



Admitting that the plate X of Bather in locrinus and Mero- 

 C7nn'us is a plate of the ventral tube, where is the anal plate? It 

 seems to us there cannot be the least doubt that in both of them, 

 and in most of the earlier Fistulata, the anal plate X is unrepre- 

 sented. Their radials are in contact laterally, and the tube does not 

 extend into the dorsal cup, but rests upon it. To satisfy ourselves 

 that the plate t forms no part of the dorsal cup, we have examined 

 and dissected a number of the most perfect specimens of locrinus 

 subcrassus, and can state positively that it is a free plate of the tube. 

 It is even perforated by lateral slits, such as occur frequently in the 

 plates of the tube, but never in the true anal plate. The tube is 

 club-shaped, narrow at the base, and its posterior side is composed of 

 large, heavy plates, which are formed into a conspicuous ridge. 

 From this narrow, arm-like ridge, as it appears from the outside of 

 the specimens, one gets no idea of the real nature of the tube, which 

 is quite deep and capacious. 



