\RT. 4 CAMBRIAN CONCHOSTRACA — ULRICH AND BASSLER 49 



ESCASONA VETUS Matthew 



Plate 1, Figure 33 



Escasona(?) veins Matthew, Canadian Rec. Sci., vol. 8, 1902, p. 458, pi. 2, figs. 

 6a, b; Geol. Surv. Canada, Rep. Cambrian Rocks Cape Breton, 1903, p. 168, 

 pi. 13, figs. 6a, b. 



The only specimen bearing this label is also too imperfect to justify 

 description. It presents obscure resemblance to E. rutellum, but the 

 pitting of its surface is of a coarser pattern. It is recommended that 

 this name and the preceding be dropped as unrecognizable. 



Occurrence. — Lower Cambrian (Lower Etcheminian, division Elc^): 

 Boundary Brook, Nova Scotia. 



Genus SELLULA Wiman 



SeUula Wiman, Bull. Geol. Inst. Upsala, vol. 6, pt. 1, 1902, p. 48. 



This genus is evidently related to Beyrichona, differing in that the 

 surface of the valve is concave with a thin ridge along the anterior 

 and posterior borders and the middle part of the anterior extremity 

 is produced into an obtuse angulation. A narrow border is present 

 along the post ventral part. 



GenoUjpe. — Sellula fallax Wiman. 



SELLULA FALLAX Wiman 



Plate 7, Figures 18, 19 



Sellula fallax Wiman, Bull. Geol. Inst. Upsala, vol. 6, pt. 1, 1902, p. 48, pi. 1, 

 figs. 31, 32. 



The characters of this the genotype and only species are given in 

 the remarks upon the genus. 



Occurrence. — Lower Cambrian, Olenellus bituminous sandstone: 

 Biludden, Sweden. 



Genus ALUTA Matthew, emended 



Aluta Matthew, Trans. New York Acad. Sci., vol. 15, 1896, p. 198. — Miller 



North Amer. Geol. and Pal., App. 2, 1897, p. 786. 

 Leperdiiia Ford (not Rouault), Amer. Journ. Sci., ser. 3, vol. 6, 1873, p. 138. — 



Walcott, BuU. No. 30, U. S. Geol. Surv., 1886, p. 146; Amer. Journ. Sci., 



ser. 3, vol. 34, 1887, p. 193; 10th Ann. Rep. U. S. Geol. Surv., 1890, p. 628. 

 Arislozoe Walcott (not Barrande), Amer. Journ. Sci., ser. 3, vol. 34, 1887, 



p. 193; 10th Ann. Rep. U. S. Geol. Surv., 1890, p. 627. 

 Bradoria Walcott (not Matthew), Proc. U. S. Nat. Mus., vol. 29, 1905, p. 99. 



Description. — Carapace bivalved, 2 to 10 mm. long; valves appar- 

 ently closing all around, leaving no gaps, obliquely acuminate-sub- 

 ovate in outhne, narrow and acuminate anteriorly, broad and rounded 

 posteriorly, straight along dorsal side; antero-dorsal angle sharp, 

 often produced, 90° or less; posterior angle more obtuse, sometimes 

 2607—31 4 



