1895,] ME. F. A. BATHEE ON TJIIfTACEIirUS. 989 



The joints between the brachials are of two kinds : perforate 

 articalation, and syzygial suture. 



The perforate articulation is represented in figs. 2, 3, 6, 7, 8, 

 9, 10 of PI. LIV. The axial canal perforates the brachial at a 

 very short distance from the bottom of the ventral groove. Two 

 parallel ridges run across the under or proximal surface of the 

 brachial, coalescing around the axial canal. These ridges fit into 

 a corresponding groove on the upper surface of the subjacent 

 brachial, which groove itself appears to be bounded by slight 

 ridges. No specimen shows a single fulcral ridge, with median 

 perforation, such as is shown in Clark's (8) pi. ii. tig. 1 e. Owing 

 to the state of preservation, and to the difiiculty of seeing more 

 than one side of any brachial, one cannot certainly distinguish 

 between the proximal and distal surfaces, except when there is 

 other evidence available. The dii-ection of the ridges is not 

 straight across the width of the brachial, but is diagonal; and I 

 think that on the distal surface the end towards the pinnule- 

 bearing side is moved dorsalwards, as is the case in Pentacrimis. 

 Since the pinnules alternate from right to left, it follows that the 

 direction of the diagonals must also alternate; so that, as is 

 actually the case, the successive diagonals must lie almost, or 

 quite, at right angles to one another (compare figs. 2 & 10 of 

 PL LIV.). This skewing of the ridges is quite obvious and well- 

 marked over the greater part of the arm ; but in the more proximal 

 region, where the brachials are still wide, and have rounded sides 

 to the ventral groove, this skewing is not so marked (PI. LIV. 

 fig. 8). A most careful search has, however, failed to disclose a 

 single brachial with a symmetry hke that of Clark's (8) pi. ii. 

 fig. 1 e, although one can find in the proximal region brachials 

 more like Schlueter's (4) pi. iv. fig. 5, a, b, which is stUl 

 asymmetrical (see PI. LIV. fig. 6). Sometimes half the ridge 

 appears to be more skewed than the other half, as in PI. LIV. fig. 8. 

 The position of the muscles and ligaments is not easy to determine. 

 There was, no doubt, a bundle of ligament-fibres on the outer or 

 dorsal side of the ridge ; and accorcling as the ridge was twisted 

 to left or right, the area of attachment for these fibres must have 

 moved alternately right and left. There is a faint depression over 

 this part of the joint-surface. One would naturally assume a 

 bundle of muscle-fibres in the area on either side of the ventra,l 

 groove, and ventrad of the ridge ; but when the ridge is skewed 

 this area becomes large on one side, and almost non-existent on 

 the other. In the larger area one can easily make out a depression 

 for the attachment of the fibres ; while in the smaller area one 

 can often distinguish a strong elongate groove, parallel with the 

 fulcral ridge, and this groove must represent the concentrated area 

 of attachment of the fibres of this side. 



It is clear that this skewing of the fulcral ridges must have 

 given the arms great power of motion, not merely up and down 

 as in Antedo7i, but from side to side. In this respect the arrange- 

 ment is analogous to that in the stem of the Bourgueticrinidae, and, 



Peoc. Zooi. Soc— 1895, No. LXIII. ' 63 



