718 CAMBRIAN BRACHIOPODA. 



Acroihyra proavia differs from A. signata Matthew, which occurs about 200 feet lower in 

 the strata of the same section, in having usually a narrower, more elongate visceral cavity, and 

 stronger callosit}^. These features, however, vary in specimens of A. proavia associated in the 

 sarnie hand specimen of shale. 



Formation and locality. — Hiddle Cambrian: (3i) Compact, fine-grained, thin-bedded gray sandstone of the 

 Paradoxides zone, on McLean Brook, 1 mile (1.6 km.) east of McCodrum Brook and 1.5 miles (2.4 km.) west of Marion 

 Bridge; (13m) sandstones of Division E3f of Matthew's [1903, p. 76] Etcheminian, on Gillis Brook, Indian River; 

 and (344] [Matthew, 1903, p. 91]) Division E3e of Matthew's Etcheminian, on the highway at V. McPhees; all in 

 eastern Cape Breton, Nova Scotia. 



(lOp) Sandstone just below the waterfall in Dugald Brook, Division E2b; (10c[) sandstones a little above lOp in 

 Division E2b; (13e) sandstones of Division E2c; (131 and 3441 [Matthew, 1903, p. 80]) sandy shales of Division E3a; 

 (13n'' and 344b [Matthew, 1903, p. 91]) sandstones of Division E3d; (13n') sandstones of Division E3e; (344a {Matthew, 

 1902b, p. 422]) sandy shales of Divinon ESc; and (344d [Matthew, 1903, p. 82]) sandy shales of Division E3f; all in Mat- 

 thew's [1903, p. 21] Etcheminian, on Dugald Brook, Indian River, eastern Cape Breton, Nova Scotia. 



,/ ACEOTHYEA SERA (MattllCw) . 



Plate LXXX, figures 4, 4a-c, 5, 5a-d, 6, 6a-i, 7, 7a-b, 8?. 



Acroihyra {signata) sera Matthew, 1902, Bull. Nat. Hist. Soc. New Brunswick, vol. 4, pt. 5, No. 20, pp. 383-384, PI. 

 XIII, figs. 3a-f . (Described and discussed as a new variety. The specimen represented by fig. 3c is redrawn 

 in this monograph, PI. LXXX, fig. 4c.) 

 Acroihyra signaia-iarda Matthew, 1902, idem, pp. 384-385, PL XIV, figs. la-d. (Described and discussed as a new 



variet}'.) 

 Acrotreta papillaia Matthew, 1902, idem, pp. 390-391, PI. XV, figs. 2a-f . (Described as a new species. Iffthe descrip- 

 tion of PI. XV the legend for figs, la-c appears as the legend for figs. 2a-c, and the legend for figs. 2a-f as the 

 legend for figs, la-f; the specimens represented by figs, la-c (on the plate) are referred to Acrotreta papillata 

 prima; and the specimens represented by figs. 2a-t (on the plate) are referred to Acrotreta papillata. The 

 description of plate is in error, the correct reference being as given in this synonymy. The specimen represented 

 by figs. 2a and 2b is redrawn in this monograph, PL LXXX, figs. 6 and 6'. 

 Acrotreta papillata var. Matthew, 1902, idem, p. 391, PL XV, figs. 3a-c. (Described. The varietal name lata is 



given to this form in the description of PL XV.) 

 Acrotreta papellata-prima Matthew, 1902, idem, pp. 391-392, PL XV, figs. la-c. (Described and discussed as a new 



variety. The thu-d reference explains error in description of plate.) 

 Acrothyra signata sera Matthew, 1903, Geol. Survey Canada, Rept. Cambrian Rocks Cape Breton, p. 56. (Notes on 



the orientation of the shells.) 

 Acrotreta papillata- prima Matthew, 1903, idem, pp. 73-74, PL III, figs. la-c. (Mentioned as a new variety, but 

 copies the original text and figures, Matthew, 1902a, pp. 391-392, PL XV, figs. la-c. The same error occurs in 

 the description of PL III as occurred in the description of PI. XV; see the third reference.) 

 Acrothyra signata sera Matthew, 1903, idem, pp. 87-88, PL I, figs. 3a-f. (Text and figures copied fromMatthew, 1902a, 



pp. 383-384, PL XIII, figs. 3a-f.) 

 Acrothyra signata-tarda Matthew, 1903, idem, p. 89, PL II, figs. la-d. (Text and figures copied from Matthew, 1902a, 



pp. 384-385, PL XIV, figs, la-d.) 

 Acrotreta papillata Matthew, 1903, idem, p. 95, PL III, figs. 2a-f . (Text and figiu-es copied from Matthew, 1902a, pp. 

 390-391, PL XV, figs. 2a-f. The same error occm's in the description of PL III as occurred in the description 

 of PL XV; see the thii-d reference.) 

 Acrotreta papillata lata Matthew, 1903, idem, pp. 95-96, PL III, figs. 3a-c. (Text and figures copied from Matthew, 

 1902a, p. 391, PL XV, figs. 3a-c.) 



Acrothyra sera differs from A. signata in the form of the visceral area and callosity, straighter 

 and nearly vertical posterior side. It is usually more elongate. Matthew [1902a, p. 383] placed 

 it as a variety of A. signata, but its characters appear to justify giving it the rank of a species. 

 A gradation m length, breadth, depth, and outline of the ventral valve and its visceral 

 area is found in specimens from the same bed of rock, that bring together Acrothyra signata seror 

 and tarda and Acrotreta papillata and its varieties lata and prima. Matthew [1902a, pp. 383-385, 

 390-392] based the above-mentioned species and varieties on differences in form of the ventral 

 valve and its visceral cavity and callosity. With his type specimens before me, and the large 

 series of specimens collected by Loper from Matthew's Division 1, assise d, and from Division 2, 

 between assise a and b, it is impossible for me to consider that more than one variable species 

 is represented. As the name sera is first in order in the original publication, it is retained for 

 the species. Also see notes under genus Acrothyra, pages. 715-716. 



