392 DR F. A. BATHER. 



more marked. The amount in millimetres is: G80, 5-2; G71, 37; G102, 6; G90, 

 6-7; G93, 13. 



§ 133. Thecal Plates. Diameters observed in i-he ordinary plates: — 



G80, holotype ..... 1 "6 mm. to 3 '8 mm. 



G87 1-8 mm. to 4-8 mm. 



G 88 . . . . . . .3 mm. to 6 mm. 



G108 2 mm. to 6-3 mm. 



There is great variation of size and shape, but the relative number of really small plates 

 is quite inconsiderable. 



Thickness of the ordinary plates, as measured by the space left between cast and 

 imprint, in Gl05 is '3 mm. 



The plates have a smooth surface, and are flat or equably curved, or, in several cases, 

 slightly swollen. In the lower part of the theca, especially near the vent, the plates 

 may sometimes show a slight, rather coarse, granulation, e.g. G79, G88 (PL II. fig. 23), 

 and more obscurely G83. 



§ 134. Stereom not preserved ; the brown powder (? iron oxide) that fills the 

 cavities shows no trace of definite structure. 



§ 135. No definite basals, but of the half-dozen or so plates adjoining the stem 

 some are often much larger than others {e.g. G7l), and their basal margin is thickened 

 and slightly rounded (PI. II. figs. 10, 11, 12, 24). 



§ 136. The adbrachial plates are proved by the hollows left behind them to have 

 been thicker than the other thecal plates (PI. II. figs. 11, 18 ; see § 133). There is no 

 such strengthening at the base of the antibrachial process. Indeed, in G96 the lower 

 part of this appears to have been telescoped in, so that six or seven plates are lying one 

 inside the other, with a distalward imbrication. In G89 (PI. II. fig. 21) one of the 

 adbrachial plates has a rounded projection near its side margin ; the bearing of this on 

 a possible hydropore has already been discussed (§ 80). 



§ 137. The Brachial Appendage appears from Gl20 (PL II. fig. 10) to have been 

 composed of four columns of wide plates, gradually arising as modifications of thecal 

 plates, and rapidly assuming a regularly alternating position with consequent hexagonal 

 outline. Two adjacent rows, apparently on the outer side (G98), are thicker and 

 shorter than the others (PL II. figs. 15, 17, 18a), and between them and the thinner ones 

 is a large lumen (fig. 186). In accordance with the views maintained above (§ 72), 

 the thicker plates are comparable with the dorsal elements of a Cystid brachiole. 



§ 138. The suture between the outer and inner series of plates may be distinctly 

 impressed (G87, PL 11, fig. 14), and this suggests a hinge-motion of the supposed 

 cover-plates. 



Several specimens indicate a distalward imbrication of the elements (PL II. 

 figs. 17, 18a) ; but since there is no trace of this in others {e.g. G87), it is probably 

 an accident of fossilisation. 



