682 CAMBRIAN BRACHIOPODA. 



ACEOTEETA CONVEXA Walcott. 



Plate LXVI, figures 6, 6a-c. 



Acrotreta convexa Walcott, 1902, Proc. IT. S. Nat. Mus., vol. 25, p. 584. (Described essentially as below as a new 

 species.) 



Shell small, subcircular, valves convex. Ventral valve most elevated at the low apex, 

 which is above the shghtly transverse posterior margin. Dorsal valve somewhat less convex 

 than the ventral valve, with its greatest elevation at the posterior third; beak minute, mar- 

 ginal. Length and width of shell 1 mm. Shell substance very thin, but not proportionally 

 thinner than other large forms. Surface marked by fine concentric striae and lines of growth. 



Casts of the interior of the ventral valve show a minute apical callosity and cardinal scars. 

 The cast of the dorsal valve has a long median furrow and minute cardinal scars. 



Observations. — This minute shell occurs in the shales and in a fine-grained interbedded 

 sandstone of the Upper Cambrian. It is characterized mainly by the convexity of the dorsal 

 valve and the relatively low ventral valve, characters that point to its descent from a form 

 like Acrotreta sagittalis. 



The cast of a dorsal valve represented by Plate LXVI, figure 6c, shows a great develop- 

 ment of the cardinal muscle scars ; this is abnormal or else the valve belongs to another species. 



Formation and locality. — TTpper Cambrian: (3n) Thin-bedded sandstone on Salmon River, Gillis Sill, 13 miles 

 (20.9 km.) south of Marion Bridge; (lOe) shales on east branch of Barachois River, 0.5 mile (0.8 km.) north of the cross- 

 road from Boisdale to Upper Leitches Creek; (101) shale on east bank of Barachois River, 6 miles (9.6 km.) from^Little 

 Bras d'Or Lake; and (101) shale in high bank on west side of Barachois River, just north of the Boisdale road; all in 

 eastern Cape Breton, Nova Scotia, Canada. 



ACEOTEETA CUEVATA Walcott. 



Plate LXVIII, figures 1, la-n. 



Acrotreta gemma Walcott (in part) [not Billings], 1884, Mon. U. S. Geol. Survey, vol. 8, pp. 17-18, PI. I, figs. Id 

 and le (not figs, la, lb, Ic, and If; see below). (Specimens now referred to Acrotreta attenuata, A. pyxidicula, 

 and A. idahoensis alta were included with the specimens representing A. curvata when this description of 

 A. gemma was written, A. idahoensis alta being figured (PL I, figs, la and lb)'. The specimens represented 

 by PL IX, figs. 9 and 9a, can not be positively located at this time, but it is probable that they should be 

 referred to A. idahoensis alta. The specimens represented by PL I, figs. Id and le, are redrawn in this mono- 

 graph, PL LXVIII, figs. Ig and 1 1, respectively. Fig. Ic represented a specimen of Acrotreta sabrinx, and 

 the specimen represented by fig. If is missing.) 



Acrotreta gemma Walcott (in part) [not Billings], 1891, Tenth Ann. Rept. U. S. Geol. Survey, p. 608, PL LXVII, 

 fig. 5b (not figs. 5, 5a, 5c, 5d, and 5e; see below). (Fig. 5b is a copy of Fig. Id of preceding reference. Speci- 

 mens now referred to Acrotreta attenuata, A. pyxidicula, A. idahoensis alta, and A. primseva were included with 

 the specimens representing A. curvata in this reference to A. gemma, but only the last two were figured; 

 A. idahoensis alta, PI. LXVII, figs. 5 and 5a, and A. primxva, PL LXVII, figs. 5c, 5d, and 5e.) 



Acrotreta gemma Hall and Clarke (in part) [not Billings], 1892, Nat. Hist. New York, Paleontology, vol. 8, pt. 1, 

 p. 102, fig. 55 (not figs. 56 and 57; see below). (Mentioned in the text and fig. 55 copied from Walcott, 1884b, 

 PL I, fig. Id. The specimens represented by figs. 56 and 57 are referred in this monograph to Acrotreta idaho- 

 ensis alta.) 



Acrotreta gemma Walcott (in part) [not Billings], 1899, Mon. U. S. Geol. Survey, vol. 32, pt. 2, p. 449, PL LXII, 

 fig. 2e (not figs. 2, 2a-d; see below). (Fig. 2e is a copy of Walcott, 1884b, PL I, fig. Id. Specimens now 

 referred to Acrotreta attenuata, A. pyxidicula, A. idahoensis alta, and A. primxva were included with the speci- 

 mens representing A. curvata when this description of A. gemma was written, but only the last two were figured: 

 A. idahoensis alta, PL LXII, figs. 2a and 2c, and A. primreva, PL LXII, figs. 2, 2b, and 2d.) 



Acrotreta curvata Walcott, 1902, Proc. U. S. Nat. Mus., vol. 25, p. 584. (Characterized essentially as below as a 

 new species.) 



This is a clearly defined species and all that is known of it, with the exception of the very 

 fine concentric surface stria?, can be illustrated. It belongs with Acrotreta idahoensis Walcott 

 and other species with a broad false area. It differs from described species in the incurved 

 apex of the ventral valve, the strong siaus of the dorsal valve, and the general aspect of the 

 two valves. 



