230 Mr. F. A. Bather on British Fossil Crinoids : 
The Tegmen is partially visible between the 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 7f 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, where 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 the 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 uncrushed stems a certain want of continuity in the ridges 
