CARADOCIAN CYSTIDEA FROM GIRVAN. 471 



Limestone series of Wharfe, and consists of an internal cast of part of the theca, and 

 external imprints of fragments of the same part. The internal cast shows the sutures 

 of certain plates in their natural relations, as shown in Reynolds' fig. 10. If that 

 fitxure be turned round, so that its straight upper line (which is not straight in the 

 fossil) is on the observer's left, and then compared with our text-fig. 7Q, the plates will 

 at once be recognised : namely, beginning at the bottom left-hand corner and following 

 the clock-hand — 8, 9, 14, 10, 5, 4, 3. It will be seen that the limiting fracture excludes 

 the pectinirhombs. Near this border are imprints of several periproctals, with a maxi- 

 mum diameter of 7 to 1 mm. Reynolds' fig. 9 represents the imprint of plate 9. A 

 squeeze taken from this shows the ornament of ridges, pustules, and very fine growth- 

 lines to resemble that of some specimens of P. Rugeri, with which species the specimen 

 also agrees in the relative width of plate 5. Mr Reynolds seems to have referred this 

 fossil to the Anomalocystidae because of certain " wavy lines." These are confined to 

 the portion which I have called an internal cast, but which is perhaps more correctly 

 described as a much decomposed and exfoliated thecal fragment. The wavy lines are 

 very irregular, anastomosing streaks of partly decomposed calcite, and their general 

 direction may be due to exfoliation along the original growth-lines, perhaps conflicting 

 with the cleavage of the decomposed stereom. To sum up, I refer this supposed A teleo- 

 cystis to Pleurocystis, and provisionally to P. Rugeri. 



§ 450. Description of Specimens. — The following remarks refer to the holotype, 

 except when otherwise stated (see PI. V. figs. 57, 58). 



The Thecal outline has been described as roughly triangular, but might better 

 be called trapezoid : the strong slope of the shoulders, forming a right angle, is the 

 characteristic feature. In the most complete individual the width at the base is 

 25*3 mm.; the sides ascend steeply for about 10 mm., then slope sharply to the narrow 

 adoral end, where the diameter, at a height of 24 mm. from the stem-attachment, is 

 6*3 mm. The other well-preserved individual must have been larger, with an estimated 

 diameter of 33 mm. at the base; from the stem-attachment to the umbo of plate 10 

 is 15 '5 mm. In the Oxford specimen the height is 15 mm., and the width is 207 mm.; 

 but both measurements are taken from the internal cast, in which the height is dis- 

 proportionately reduced (PI. V. fig. 59). 



§ 451. Salter's words : " The basal plates project over the stem considerably," and 

 the representation of this region in Bone's figure scarcely convey a correct idea of the 

 facts. The projecting rim of what appears to be the proximal columnal is visible in the 

 middle of both faces ; but plates 2 and 3 send a wing-like process downwards on each 

 side of the theca to below the level of the third columnal. In the larger individual 

 this distance amounts to 2 '8 mm. 



§ 452. Of the plates on the antanal face, 5, 6, and 9 are all wider than high, 

 5 being 87 mm. by 11*3 mm. The umbones of 6 and 9 project at the sides of the 

 theca, which here has a width of 25*3 mm. The surface of 5 is relatively flat, and its 

 umbo does not project. The umbo of 10 projects strongly, and that of 11 only a little 



TKANS. ROY. SOC. EDIN., VOL. XLIX., PART II. (NO. 6). 62 



