398 Mr. F. A. Bather on British Fossil Crinoids: 



based on seven specimens : — Height 3'36 millitn. ; greatest 

 width 3*7 millim. 



Eadials, 5, of normal shape ; project slightly from the cup, 

 so that the articular facet, lying at right angles to the outer 

 surface of the plate, is directed outwards ; sometimes show 

 traces of axial folding. Measurements, based on seven speci- 

 mens : — Height to bottom of facet 2*9 millim. ; greatest 

 width 4"21 millim. The facet occupies from less than ^ to f 

 of the width of the radial ; its average width as deduced from 

 the same seven specimens is 2*26 millim. The articular 

 surface is rarely exposed, and when visible is usually so worn 

 that no drawing of it can be given : it appears, however, that 

 the axial canal was not separated from the ventral groove by 

 stereom, that a transverse ridge running at the level of the 

 axial canal served as fulcrum, that outside this ridge there 

 was a bevelled surface marked with slightly radiating rugo- 

 sities, and that inside the ridge on either side of the groove 

 was a depression for a muscle-attachment. Compare with 

 articular surface of first costal (PI. XIII. fig. 10) . On either 

 side the facet the distal portions of the radial curve round it 

 and bend inwards to meet the tegmen. 



A rmSj about six times as long as the cup : each splits into 

 two main branches, which bear pinnules, one on each ossicle 

 on alternate sides ; of elegant appearance. The younger tlie 

 individual the more marked is the axillary character of the 

 ossicles of the main arm, which thus has an irregular zigzag 

 appearance (PL XIII. fig. 5) ; in older specimens the main 

 arm is more straight and regular, but the sutures between its 

 ossicles alternate markedly in direction. These differences of 

 character may also to some extent be traced within a single 

 arm, where the distal end corresponds to the younger, the 

 proximal to the older stage. 



Costals usually 3 or 4 to a ray ; rarely more, 136 Holcroft 

 has 6 in one ray, very rarely less ; usually all are of the same 

 width as the radial facet, but sometimes, as in 349 Holcroft, 

 they taper distalwards. The axillary of course always 

 broadens out. The height of each costal is f its width, 

 except in the axillary, where the t^vo a]-e equal. 



The pinnules do not begin their regular arrangement immed- 

 iately after the bifurcation of the arms. The first distichal 

 never appears to bear a pinnule, but the first pinnule arises on 



iu any case it seems advisable to liave a definite term to express it. 

 Since the main ridges or folds appear to follow the lines of the axial 

 nerve-cords, I venture to speak of them as "axial " in direction, and to 

 call the phenomenon generally " axial folding."' 



