CARADOCIAN CYSTIDEA FROM GIRVAN. 465 



§ 408. Pleurocystis squamosa var. rohusta. 

 (Text-fig. 66.) 



1854. Pleurocystites robustus E. Billings, Canad. Journ., vol. 2, p. 252, f. 15. 



1857. Pleurocystites robustus Bill., E. Billings, Geol. Surv. Canada, Rep. Progr., 1856, p. 287. 



1858. Pleurocystites robustus Bill., E. Billings, Canad. Org. Rem., dec. 3, p. 49, pi. .1, f. 2a. 

 1899. Pleurocystites squamosus Bill., O. Jaekel, " Stammesgesch. d. Pelmat.," p. 234 (as syn.). 



§ 409. Diagnosis. — A P. squamosa larger than the norm of the species. 

 Pectinirhombs concave, with border strongly raised and more rounded than in norm ; 

 in 10-14 sutural axis : transverse axis : : 6 : 7 (as compared with 6 : 9 in norm). Orna- 

 ment of antanal face, obscure radiate ridges, and fine rhombic striae. 



§ 410. Locality. — Ottawa, E. Billings. ? Hull, P.Q., colld. W. R. Billings, 

 Brit. Mus. E 16039. ?? Kirkfield, Ont, colld. W. A. Parks, Brit. Mus., E 15899. 



§ 411. Horizon. — Trenton Limestone. 



§ 412. Tjrpe-material. — The single fragment figured by Billings (1854) is the 

 holotype. "The few fragments" mentioned by him in 1858 were collected later. 



§413. Remarks. — A British Museum fragment from Kirkfield, Ont. (E 15899), 

 which I am inclined, by reason of its large size, to refer to this variety, shows no 

 pectinirhomb 1-5 ; but there is some damage to the surface in that region, and there 

 may have been a small one. 



E.Billings was himself uncertain as to the distinctness of this form from P. squamosa, 

 h was definitely and without discussion made a synonym of that species by Jaekel. 

 The difi"erences may be those of old age, but, pending the discovery of further material, 

 it seems well to retain the name as that of a variety. 



§ 414. Pleurocystis filitexta. 

 (Text-figs. 61, 62, 68.) 



1854. Pleurocystites fiUtextus E. Billings, Canad. Jouru., vol. 2, p. 252, ff. 13, 14. 



1857. Pleurocystites filitextus Bill., E. Billings, Geol. Surv. Canada, Rep. Progr., 1856, p. 286. 



1858. Pleurocystites filitextus Bill., E. Billings, Canad. Org. Rem., dec. 3, p. 50, pi. 2, ff. la, b. 

 1858. Pleurocystites elegans Bill., E. Billings, Canad. Org. Rem., dec. 3, p. 51, pi. 2, f. 2d 



(caet. excl.). 

 1881. Pleurocystites filitextus Bill., W. R. Billings, Trans. Ottawa Field-Nat. Club, vol. 1, 



No. 2, p. 34. 

 1896. Pleurocystis filitexta Bill., E. Haeckel, "Amph. und Cyst.," Festschr. Gegenbaur, vol. 1, 



p. 44, pi. 2, ff. 15, 16. 



1899. Pleurocystites filitextus Bill, 0. Jaekel, "Stammesgesch. d. Pelmat.," p. 232, f. 45; 



p. 234, pi. 12, ff. 3-5 (pars). 



1900. Pleurocystis filitextus [sic] Bill., F. A. Bather, "Treatise on Zoology: Echinoderma," 



p. 65, f. 34. 

 1911. Pleurocystis filitextus Bill., E. Kirk, Proc. U.S. National Mus., vol. 41, pi. 2, f. 4, pi. 3, f. 3. 



§ 415. Diagnosis. — A Pleurocystis with thecal sides curved ; shoulder-angle 45°-50° ; 

 ratio, width : height, of theca, circa 7 ; of plate 5, circa '85 ; plate 3 level with stem- 

 attachment, or scarcely passing below proximal flange. Pectinirhombs all present, flat 



