ART. 4 CAMBRIAN CONCHOSTRACA — ULRICH AND BASSLER 17 



respect with B. vigilans mut. obesa Matthew, which is regarded as a 

 good species and not a mere mutation. Finally, specimen C repre- 

 sents a distinguishable variety of B. vigilans s. s. described on a fol- 

 lowing page as B. vigilans concentrica. 



The most striking feature common to all three specimens is the 

 sharp definition and unusual prominence of the ocular tubercle. It 

 is a more conspicuous feature even than would appear from the figure. 

 In other respects the illustrations are fau'ly accurate for the typical 

 form (specimens D and E). Compared with other species of the 

 genus, the outline of this is peculiar in being rather narrowly rounded 

 posteriorly and in the cardinal and ventral portions being more nearly 

 parallel than in any of the others known. The anterior edge is some- 

 what thickened, the posterior end of the hinge projects as a thick 

 blunt spine, and the surface punctation is rather fine. The affinities 

 of the species as here restricted are with B. scrutator and B. benepunda, 

 differing from both in the narrow posterior part in having a post- 

 cardinal spine, a more prominent ocular tubercle, and finer surface 

 punctae. As to the supposed mutation obesa, it is regarded as a very 

 different species with relations to B. cambrica and B. spectator, rather 

 than B. vigilans. 



Occurrence. — Lower Cambrian (Upper Etcheminian division E26, 

 EZd, E3e): Dugald Brook, Cape Breton, Nova Scotia. Walcott 

 localities 10^, 13w", ISn". 



Cat. No. 50525, U.S.N.M. 



BRADORIA VIGILANS CONCENTRICA, new variety 



Plate 3, Figures 18, 19 



Bradoria vigilans Matthew (part), Bull. Nat. Hist. Soc. New Brunswick, No. 

 18, 1899, p. 205; Canadian Record Sci. vol. 8, 1902, p. 454; Geol. Surv. 

 Canada, Rept. Cambrian Rocks Cape Breton, 1903, p. 164. 



This new variety is represented by weU-preserved specimens in the 

 Walcott collection and by one of the types (C) of Matthew's Bradoria 

 vigilans. Variety concentrica differs from the typical form of B. 

 vigilans (1) in the more concentric arrangement of the surface punctae, 

 a rugulose aspect being observable toward the edges, and (2) in the 

 broader, thicker, straighter, and more nearly vertical trend of the 

 anterior margin. The new variety suggests affinities to species of the 

 B. rugulosa section, the approximation being toward B. ovalis rather 

 than any of the other species of that section. 



Occurrence. — Lower Cambrian (Upper Etcheminian, division E3(/) : 

 Dugald Brook, Cape Breton, Nova Scotia. (Walcott locality I'^n" .) 



Cotypes.— Cat. No. 50527 U.S.N.M. 

 2607—31 2 



