CARADOCIAN CYSTIDEA FROM GIRVAN. 395 



complete, are more than twice as long as the theca. It seems safe to accept the propor- 

 tion 3 : 1 as generally correct, and to infer that it did not decrease with advancing age. 

 This proportion is the same as in D. Sedgwicki. 



§ 146. In the Distal region the dimeres abut, with scarcely a trace of alternation, 

 tQ form a cylinder tending to a dice-box shape. In Gl05 (PI. II. fig. 19) the lengths 

 of these columnals, starting from the proximal end, are 4"3. 6"8, 7'6. 7'8, 7*8, 6*4, 5, 

 4*3 mm. The diameters of the more proximal are 2 3 mm. at their ends, and 2*1 mm. 

 in the constricted middle ; thence the stem tapers gradually to a diameter of 1 '6 mm. 

 near the broken distal end. The lumen of each columnal also has a dice-box shape, 

 rather more emphasised, the respective measurements being 1'2 mm. and '6 mm. 



§ 147. The Median region constitutes merely a very rapid transition to — 



§ 148. The Proximal region, well seen in GIOd and G90 (PI. II. figs. 19 and 20). 

 The measurements given above (§ 145) are slightly increased by the crushing of the 

 specimens. In the holotype, Gr80, the width of the stem-attachment is 10"5 mm. 



The region consists of four vertical columns, arising by dichotomy of the distal 

 dimeres ; each is composed of about ten plates, which are thin, wider than high, alter- 

 nating, and consequently of hexagonal outline. Each has a rounded flange towards its 

 lower margin, more marked in those nearer the stem, and sometimes slight subsidiary 

 ridges. In G70 the flanges are ornamented with vertical ( = axial) granular ridges, as 

 in Pleurocystis. There is often a tendency to imbrication, the more proximal plates 

 overlapping the more distal, e.g. G93. 



The proximal region does not merge into the theca (cf § 87). 



§ 149. Comparison with Dendrocystis Sedgwicki and D. Barrandei. — The marked 

 extension of the lobes gives to the theca a width nearly half as great again as the 

 height, instead of equal to or less than the height. In absolute thecal height the 

 species is about half-way between the two others. The antibrachial process is a very 

 distinctive character. In the absence of folded plates and in the paucity of very 

 small plates, D. scotica agrees with D. Bai'randei, but differs from both species in the 

 greater absolute size reached by the plates, and perhaps in the occasional granular 

 ornament (§ 133). 



The brachial appendage is relatively and absolutely much longer, and in width 

 resembles that of D. Barravdei rather than of D. Sedgivicki ; it is more sharply 

 separated from the adbrachial plates of the theca. (See further § 63.) 



If the sugar-loaf plate and its surroundings really are connected with the vent in 

 the Bohemian species, then D. scotica differs from them both in the position of the 

 anus and in the shape of the periproctal plates. 



The stem, though retaining the same relative length as in D. Sedgwicki, is rather 

 narrower in the distal region, and the dimeres have almost lost all trace of alternation. 

 The constriction of the distal columnals and of their lumen, the almost complete sup- 

 pression of the median region, and the regular structure of the proximal region are all 

 characteristic features. 



