220 ]\Ir. F. A. Bather on British Fossil Crinoids : 



less ; it is rounded and somewhat swollen above (PI. XIII. 

 figs. 1, 2, 6, 9). The plates of which it is composed are 

 hexagonal in the proximal region, but distally they become 

 irregular in outline. The size of the plates varies consider- 

 ably, but tlieir transverse diameter is as a rule between I'o 

 and 2'5 niillim,, their vertical diameter being rather less. 

 The plates are sometimes quite smoothly rounded or almost 

 flat (PI. Xlll. fig. 1) ; sometimes they are slightly folded at 

 the edges, the folds being at right angles to the sutures 

 (PI. XIII. ^^. 9): in E G002 this folding is very clearly 

 marked, and at the same time it is quite obvious that there 

 are no pores or slits within the folds (PI. XIII. fig. 8). In 

 the separate distal end of a sac shown in PI. XIII. tig. 6, the 

 surface of the ])latcs appears rather curiously pitted ; this, 

 however, is no doubt due to weathering, and may be com- 

 pared with the roughness already alluded to (PI. XIII. fig. 7). 

 The Tegmen is unknown. 



The Stem (PI. XIII. figs. 1 and 13; zincotype, p. 211, 

 figs. 2 and 3) is round, composed of ossicles which alternate 

 both in height and width with fair regularity. The following 

 are a few measurements of the heights of the ossicles : — In 

 E 6004 (fig. 2, p. 211) the respective heights of the ossicles 

 are about 1-16 millim. and '59 millim. ; in 57362 B. M. they 

 are 1 millim. and '55 millim. ; in 07364 B. M., in a more 

 proximal part of the stem, the ossicles are of three sizes with 

 lieights 1 millim., '75 millim., and '2 millim. The width of 

 the stem is between 5 millim. and 7 millim. The lumen is 

 quinquelobate and its diameter is about ^ that of the stem, or 

 a little less. The articular surface of each ossicle is slightly 

 concave, and is radiately striated. In the longitudinal sec- 

 tion the space between the concave articular surfaces is filled 

 with transjiarent calcite, while the lumen itself is filled with 

 opaque matrix. This probably results from the fact that the 

 interarticular ligaments decayed more gradually than the 

 axial cord and its blood-vessels, and that, after the place of 

 the latter had been taken by infilling ooze, they themselves 

 were gradually replaced by the infiltration of carbonate of 

 lime. We may now note, both in the longitudinal and trans- 

 verse (fig. 3) sections, that the stereom of the ossicles is 

 separated from the matrix in the canal by a thin film of 

 calcite; this too, then, must represent some lining membrane 

 or ligament. 



The base of the cup is often slightly excavated for the top 

 columnal (PI. XIII. fig. 4). 



