ACEOTRETIDiE. 719 



Formation and locality. — Middle Cambrian: (lOp') Sandstone 0.25 mile (0.4 km.) from the lower bridge on 

 Gregwa Brook, Indian River; (lOp") sandstone on the small brook on the hill between the bridge over Indian River 

 and McPhees Brook; (13k) shales of Matthew's [1903, p. 15] Coldbrook, above the great fall in Dugald Brook, Indian 

 River; and (344e [Matthew, 1903, p. 78]) shales of Division Eld of Matthew's [1903, pp. 28 and 29] Etcheminian, on 

 Boundary Brook, eastern side of the Escasonie Indian Reservation; all in eastern Cape Breton. 



(344g [Matthew, 1903, p. 77]) Shales of Division Elc; (13t") sandstones of Divisions Elc and Eld; (13f) sandstones 

 20 feet (6 m.) above Division E2a; (ISd') sandstones opposite the third waterfall in Dugald Brook, between Divisions 

 E2a and E2b; (lOp) sandstones just below the waterfall in Division E2b; and (13e) sandstones of Division E2c; all in 

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



Shells somewhat doubtfully referred to Acrothyra sera occur at the following localities : 



Middle Cambrian: (13p) Sandstones 40 feet (12.2 m.) above Division E2a; and (13p') sandstones 45 feet (13.6 m.) 

 above Division E2a; both in Matthew's [1903, p. 21] Etcheminian, on Dugald Brook, Indian River, eastern Cape 

 Breton, Nova Scotia. 



Acrothyra signata Matthew. 



Plate LXXX, figures 1, la-d. 



Acrothyra signata Matthew, 1902, Bull. Nat. Hist. Soc. New Brunswick, vol. 4, pt. 5, No. 20, pp.' 381-382, PI. XIII, 



figs. 2a-e. (Described and discussed as a new species, see below for copy of the greater part. The specimens 

 represented by figs. 2b and 2c are redrawn in this monograph, PI. LXXX, figs. 1 and Id, respectively.) 

 Acrothyra signata Matthew, 1903, Geol. Survey Canada, Rept. Cambrian Rocks Cape Breton, p. 87, PL I, figs. 2a-e. 

 (Text and figures copied from preceding reference.) 



Matthew's description [1902a, p. 381] of the interior of the two valves is as follows: 

 There is a strong narrow callus, one-third of the length of the valve, bounded by a raised ridge at the sides and in 

 front; at the front of this callus is an oval pit, from which a groove runs backward nearly to the apex of the shell, where 

 it is supposed to connect with the foramen. Outside the callus, on each side, near the margin of the valve, are len- 

 ticular marks of the lateral muscles. About the middle of the valve the position of the anterior adductors is indicated 

 by a faint impression of the lozenge or "heart-shaped " depression. * * * 



* * * This shows a sharp, thin, median septum for haU of the length of the valve. This ridge is broader and 

 more distinct at the front; at each side are lateral obscure ridges, diverging from the umbo. Outside of these ridges 

 are the lenticular imprints of the lateral muscles. 



The only modification to be made is in leaving out the word "narrow" before "callus" 

 in the description of the ventral valve. The callosity is strong and relatively broad. 



Among the type specimens received from Doctor Matthew one ventral valve is elongate, 

 like the type figured by him. Two other ventral valves are shorter, like our figures 1, la-b. 

 The dorsal valves are similar in the material received from Doctor Matthew and that illustrated 

 by him, and in the collection made by Mr. S. Ward Loper. 



A. signata differs from A. proavia (Matthew) in the less elongate, narrow visceral cavity 

 and apical callosity of the ventral valve. It occurs at about 200 feet lower in the strata, accord- 

 ing to Matthew, who [1903, pp. 23-27] gives a detailed section of the beds and lists of fossils 

 occurring at each faunal zone. 



Matthew [1902a, p. 382] found this species in his Division Elb. Loper collected it from 

 Matthew's Division Eld; also in abundance between Divisions E2a and E2b on Dugald Brook. 

 Formation and locality. — Middle Cambrian: (13t) Sandstones at the base of Division Elb; (344k [Mattheio, 

 1903, p. 77]) sandstones of Division Elb; (13f ) sandstones of Divisions Elc and Eld; (13d') sandstones opposite the 

 third waterfall in Dugald Brook, between Divisions E2a and E2b; (lOp) sandstones just below the waterfall in Divi- 

 sion E2b; all in Matthew's [1903, p. 21] Etcheminian, Dugald Brook, Indian River, eastern Cape Breton, Nova Scotia. 



^ Acrothyra signata orta Matthew. 

 Plate LXXX, figures 3, 3a-b. 



Acrothyra signata orta Matthew, 1902, Bull. Nat. Hist. Soc. New Brunswick, vol. 4, pt. 5, No. 20, pp. 385-386, PL 

 XIII, figs. 4a-f. (Described and discussed as a new variety. The specimens represented by figs. 4a and 4c 

 are redrawn in this monograph, PL LXXX, figs. 3a and 3b, respectively.) 



Acrothyra signata orta Matthew, 1903, Geol. Survey Canada, Rept. Cambrian Rocks Cape Breton, pp. 89-90, PL I, 

 figs. 4a-f. (Text and figures copied from the preceding reference.) 



A. signata orta differs from A. signata Matthew in its more elongate form and narrow 

 visceral area, characters that place the variety near A. proavia (Matthew). Its shorter visceral 

 area distinguishes it from A. proavia. In the absence of specimens showing the interior of 

 the ventral valve there is no way of distinguishing A. proavia from A. signata orta. 



