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



The Tegmeii is partially visible between tlie arms and on 

 either side the origin of the ventral sac, in 57478 a and h and 

 153 Mason College. The portions observed are composed of 

 small plates of various sizes in which no definite arrangement 

 can be distinguished. The tegmen was evidently flexible, and 

 stretched up the arms, in some cases, if not in all, to the end 

 of the distichals (PL X. fig. 5 and Diagram 1). 



The Stem is almost perfect in specimen 48049 B. M. 

 Here its length is 19'5 centim., or about 7| inches. It has 

 a breadth of 5 millim., which at the proximal end widens to 

 7 millim. The distal end is imbedded in a congeries of frag- 

 ments which seem to have belonged to radical cirri. It is 

 round except at its extreme proximal end, where it tends to 

 become pentagonal, with its angles, as in all Dicyclica, inter- 

 radial. The ossicles are only '25 millim. high at the distal 

 end, i. e. 100 run to the inch ; they gradually increase in 

 height, till, about halfway up the stem, they are two to the 

 millimetre : here, however, an alternation of size sets in, 

 which increases as the proximal end is approached, so that in 

 that region the large ossicles are twice as high as the small 

 ones. At the same time the ossicles become more ridged, 

 and the alternation of size increases the effect of the ridging. 

 The articular surfaces of the ossicles were, as indicated by 

 specimen 144 Mason College, covered with fine radiating 

 ridges. The lumen was circular or slightly pentagonal with 

 radial angles. In specimen 57478 a, where, at 25 millim. 

 from the calyx, the diameter of the stem is 5 millim., that of 

 the lumen is 3 millim. ; in 57478 5, at 5 millim. from the 

 calyx, M'here the diameter of the stem is 7 millim., that of 

 the lumen is 4 millim. (Diagrams 5 & 7). 



Owing to the large size of the lumen, the stem is often 

 flattened, and this in many cases has produced cracks in the 

 stem. These cracks do not, however, appear to be merely 

 accidental. They are invariably radial in position, and con- 

 tinue for long distances ; this is well shown in 48049 B. M. 

 and in Mr. Madeley's specimen. In 48049, although the 

 stem is hardly if at all crushed, two such radial cracks may 

 be traced from the distal end for 15 centim., or nearly 6 inches, 

 along the stem ; they are especially clear at tlie distal end. 

 It seems therefore pretty certain that these cracks represent 

 sutures : in all Dicyclica with a quinquepartite stem the 

 sutures are radial. It is true that a thin section of the 

 column of 57478 a does not show them ; but here they have 

 probably been obscured by fossilization. On the other hand 

 in uncruslied stems a certain want of continuity in the ridges 



