466 DR F. A. BATHER. 



or slightly concave, with slight border, all elongate, of lanceolate or subrhomboidal outline; 

 in 10-14, sutural axis : transverse axis : : 2 : 1 ; folds in all uncovered. Plates 12 and 14 

 meet below plate 18 in a well-defined suture. Periproctals average 27 mm. in diameter, 

 and show no lessening in size near the margin. Ornament of antanal face variable : 

 radiate ridges, and minor but well-marked rhombic ridges, sometimes crossed by con- 

 centric ridges, and in places irregularly granular. Columnals vertically ridged on 

 flanges and swellings, but less than in P. squamosa. 



§ 416. Locality.— Ottawa, E. Billings, Brit. Mus. E7600 ; Hull, P.Q., colld. 

 W. R. Billings, Brit. Mus. (E16040-E 16044), colld. W. R. Smith (E16046, E16047). 



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



§ 418. Type-material. — The original of E. Billings' fig. 13 (1854) is the holotype. 



§ 419. Remarks. — It is believed ihsit P. filitexta., P. elegans, and P. exornata differ 

 from the other Ontario species in, at any rate, the greater size of their periproctals. 

 Whether they differ intei- se is a question on which previous authors are not agreed. 

 Thus E. J. Chapman (Jan. 1859, p. 45) thinks that P. elegans "may prove . . . mere 

 variety of P. JiUtextus." E. Billings was himself doubtful whether his pi. 2, f. 2d 

 (1858), a crushed specimen, belonged to P. elegans or P. Jilitexta ; but W. R Billings 

 (1881, p. 34), while maintaining the distinctness of the two species, referred the 

 specimen in question to P. Jilitexta. Jaekel (1889, p. 234), without discussion, makes 

 the two species synonymous. 



P. exornata is regarded by Dr Jaekel {loc. cit.) as a variety of P. Jilitexta ; but if 

 it was rightly supposed to come from a lower horizon, its retention of specific rank 

 is convenient (§ 426). 



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



§ 420. Pleurocystis elegans. 



(Text-fig. 67.) 



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



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



ff. 2a-c (non d). 



1859. Pleurocystites elegans Bill. ?var. of fiUtextus Bill., E. J. Chapman, Canad. Journ., 



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

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



No. 2, p. 34. 

 1899. Pleurocystites fiUtextus Bill, (pars), 0. Jaekel, " Stammesgesch. d. Pelmat.," p. 234. 



§ 421. Diagnosis. — A Pleurocystis with sides of theca straight and almost parallel, 

 the left side continuous with the shoulder ; shoulder-angle ca. 60° ; ratio, width : height, 

 of theca, circa "83 ; of plate 5, circa "9 ; plate 3 descends to about second flange. 

 Pectinirhombs all present, with well-marked border, all regularly rhomboidal or almost 

 lozenge-shaped; 10-14 and 11-12 elongate, 1-5 widened, all much shorter in relation 

 to suture than in P. Jilitexta [ratios uncertain] ; folds in all uncovered. Anal face 

 undescribed ; periproctals presumed large as in P. Jilitexta [but W. R. Billings (1881) 



