OARADOCIAN CYSTIDEA FROM GIRVAN. 467 



says their size affords " excellent specific means of distinction "]. Ornament of antanal 

 face radiate and rhombic ridges, stronger than in P. JiliteMa. 



1 402. Locality. — Ottawa, E. Billings; Hull, P.Q., Brit. Mus., colld. W. R. 

 Billings (E16037), colld. J. Stewart {E7535) ; Belleville, Ont., colld. W. R. Smith 

 (E15924). Brit. Mus. E7683 (text-fig. Q>7) was presented by Lady Dufferin, and its 

 locality is unknown. 



5 423. Horizon. — Trenton Limestone, probably Horizons 5 and 2 (see § 406). 



S 424. Type-material. — The specimen definitely mentioned by E. Billings (1857) 

 as in the Museum of the Geological Survey, Ottawa, is the holotype. 



§ 425 Remarks.— Now that Mr Walter Billings has referred E. Billings' fig. 2(i 

 to P.filitexta, there is no difficulty in discriminating between the two species (§ 419). 



In the absence of definite information as to the periproctals, the difference between 

 this species and P. squamosa var. rohusta seems to lie only in the shape of the pectini- 

 rhombs ; 10-14 is almost lozenge- shaped and elongate along the suture in P. elegans, 

 but in P. rohusta is subrhomboidal, almost triangular, and widened across the suture. 



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



§ 426. Pleurocystis exornata. 



1857. Pleurocystites exornatus E. Billtngs, Geol. Surv. Canada, Rep. Progr., 1856, p. 287. 



1858. Pleurocystites exornatus Bill., E. Billings, Canad. Org. Rem., dec. 3, p. 52. 



1859. Pleurocystites exornatus (et errore ornatus) Bill., '?var. oijilitextus Bill., E, J. Chapman, 



Canad. Journ., n. ser., vol. 4, p. 45. 

 1899. Pleurocystites filitextus, var. exornata Bill., O. Jaekel, " Stainmesgesch. d. Pelmat.," 

 p. 234. 



§ 427. Diagnosis. — A Pleurocystis [with shape of theca undescribed]. Pectini- 

 rhombs all present, flat, with sharp border, all widened and sub-triangular [ratio 

 undescribed]. Anal face and periproctals as in P. filitexta. Ornament of antanal face 

 [not described, but inferred from the name to be] clearly, if not strongly, marked. 

 Columnal flanges vertically ridged. 



§ 428. Locality. — Near Montreal. 



§ 429. Horizon. — Lower part of Trenton Limestone, and fragments (?) in Chazy 

 Limestone (Billings, 1858). 



§ 430. Type-material. — ^The specimen definitely mentioned by E. Billings (1857) 

 as in the Museum of the Geological Survey, Ottawa, is the holotype. 



§ 431. Remarks. — The diagnosis is incomplete, since many of the characters were 

 not mentioned by E. Billings, and the specimen has never been figured. The shape 

 of the rhombs is, however, quite enough to separate the species from P. filitexta and 

 P. elegans (see § 419). 



I can find no subsequent reference to the occurrence of this species, or indeed of 

 this genus, in the Chazy. Dr Ami did not mention it in his brief synopsis of the 

 geology of Montreal (Dec. 1887). 



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



