ART. 4 CAMBKIAN CONCHOSTRACA — ULRICH AND BASSLER 47 



The species, as judged from a large number of specimens in the 

 Walcott collection, is rather variable in the relative proportions of 

 height and length. 



Occurrence. — Middle Cambrian (Johannian, division C2h) : McLean 

 Brook, near Marion Bridge; Dugald Brook; and 1.5 miles west of 

 Marion Bridge, Cape Breton, Nova Scotia. 



Plesioty pes. —Cat. No. 50502-50504, U.S.N.M. (3i, 10s, 13g). 



BEYRICHONA OVATA Matthew 



Plate 7, Figure 10 



Beyrichona ovata Matthew, Trans. New York Acad. Sci., vol. 14, 1895, p. 135, 



pi. 7, fig. 8. 

 Escasona ovata Matthew, Canadian Rec. Sci., vol. 8, 1902, p. 458 (gen. ref.) 



The original type of this species (it is accompanied by a second 

 specimen too poorly preserved to be identified) is a Beyrichona wdth 

 an extremely short hinge. On account of this shortening of the 

 carapace, the median dorsal depression is very narrow, and, being 

 deep, the central swelling observed in the more typical species is 

 entirely obsolete. The antero-cardinal node, however, is as in 

 B. tinea, while the parts in which it differs are behind this node, 

 hence in those portions of the carapace which the variations in the 

 more typical species of the genus show to be comparatively unstable. 

 In short, while B. ovata is a well marked and good species, it is yet 

 a Beyrichona. Matthew's figures are fairly accurate. 



Occurrence. — Lower Cambrian (Hanfordian, division Cl62): Han- 

 ford Brook, New Brunswick. 



BEYRICHONA FABA Wiman 



Plate 7, Figure 17 



Beyrichona f aba Wiman, Bull. Geol. Inst. Upsala, vol. 6, pt. 1, 1902, p. 47, pi. 3, 

 fig. 52. 



Although imperfect the type specimen of Beyrichona f aba, judging 

 from the original illustration here reproduced closely approaches in 

 outHne certain American species such as B. tinea planata Matthew. 



Occurrence. — Lower Cambrian, Olenellus bituminous sandstone: 

 Limon near Gefle, Sweden. 



BEYRICHONA GEVALENSIS Wiman 



Plate 7, Figures 14-16 



Beyrichona gevalensis Wim.\n, Bull. Geol. Inst. Upsala, vol. 6, pt. 1, 1902. p. 46, 

 pi. 1, figs. 29, 30, 35. 



Wiman's figures are so similar to American species Hke B. tinea 

 that there can be no doubt of the correct reference of this species 

 to Beyrichona. 



Occurrence. — Lower Cambrian, Olenellus bituminous sandstone: 

 Biludden, Sweden. 



