CARADOCIAN CYSTIDEA FROM GIRV^AN. 469 



From the vague description of the periproctals and from the form of the pectini- 

 rhombs, one infers, with Miller & Gurley, that the species is nearest to P. squamosa. 

 From this it appears to differ in the more ovate outline of the theca and the more 

 elliptical shape of the pectinirhombs. Further, according to the statement of Miller 

 & Gurley, " this species has one plate less in the first range." Interpreting this 

 by the figures, one gathers that plate 1 is very low, but is extended to the right, round 

 the edge of the theca, so as to cut plate 2 off" from the stem. It certainly seems 

 improbable that plate 2 should not come down to the stem on the anal face, but on the 

 antanal face plate 1 may very well have the shape shown. Dr Jaekel, indeed (1899, 

 p. 235), says that the remarks of the authors on this point are " off'enbar irrthiimlich. " 

 A precise statement supported by a drawing is, however, not to be dismissed without 

 examination of the actual evidence ; and I have not seen the holotype. 



Comparison with other Species. — See §§ 551-553. 



§ 444. Pleurocystis Rugeri. 

 (PL V. figs. 57, 59. Text-fig. 69.) 



1866. Pleurocystites Rugeri J. W. Salter, Mem. Geol. Surv. Gt. Britain, vol. 3, p. 288, 



pi. 23, f. 5. 

 1878. Pleurocystites Rugeri Salt., " Mus. Pract. Geol., Catal. Camb. Foss.," pp. 35-63. 

 1899. Pleurocystites Rugeri Salt., 0. Jaekel, " Stammesgesch. d. Pelmat.," p. 235. 

 1902. Pleurocystites Rugeri Salt., H. A. Allen, Geol. Surv. U.K., Summ. Progr., p. 205. 



§ 445. Diagnosis. — A Pleurocystis with theca of trapezoid outline, the sides diverg- 

 ing ; shoulder-angle ca. 90° ; ratio, width : height, of theca, "95 ; of plate 5, 1"3 ; plate 

 3 descends to about third flange. Pectinirhomb 1-5 suppressed; 10-14 and 11-12 

 slightly convex, no definite border, both widened, long-elliptical; in 10-14, sutural 

 axis : transverse axis : : 3 : 13; folds uncovered. Periproct reaches between plates 12 

 and 14 almost up to the brachioles. Periproctals generally about "65 mm. in diameter, 

 but near margin may be as low as "4 mm. Ornament of antana] face, fine granules in 

 concentric lines, and in main and subsidiary axial ridges, also slight radiate ridges. 

 Columnal flanges bear granules in irregular vertical ridges. 



§ 446. Locality. — ^The holotype is from Blaen-y-Cwm, near Llangadoc, near 

 Llandovery, S. Wales. From Cefn-Llwydlo near Llandovery come Nos. 25831 and 

 25832 of the Museum of Practical Geology. M.P.G., No. 964 and the Oxford specimen 

 are from Cynwyd near Corwen. M.P.G., Nos. 25702 and 25703, which are probably 

 of this species, come from Haverfordwest. "A stream south of Wharfe," Yorkshire, 

 is the locality of a doubtful specimen in the Sedgwick Museum (see end of § 449), 



§ 447. Horizon. — Except the last, all the specimens from the localities just 

 mentioned are in an occasionally micaceous sandstone or grit said to be Caradoc Sand- 

 stone. The matrix from the type-locality is a dark grit with grains or small pebbles of 

 white quartz up to 5 mm. diameter. Prof. 0. T. Jones (in litt.) confirms the Caradoc 

 age of the fossils from this locality in general, but the precise horizon within the 



