AET. 4 CAMBRIAN CONCHOSTRACA — ULRICH AND BASSLER 31 



BRADORIA NITIDA (Wiman) 



Plate 3, Figure 16 



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

 pi. 1, figs. 34, 36, 37. 



The illustration of the type of Bradorona nitida Wiman, reproduced 

 on Plate 3, indicates that it belongs to Bradoria and is not unlike 

 certain of the American species. 



Occurrence. — Cambrian sandstone: Island of Aland, Sweden. 



BRADORIA mCKSU (Jones) 



Plate 3, Figure 4 



Leperditia hicksii Jones, Quart. Journ. Geol. Soc. London, vol. 28, 1872, p. 183, 

 pi. 5, fig. 16; Ann. Mag. Nat. Hist., ser. 5, vol. 8, 1881, p. 346, pi. 20, fig. 6. 



As figured this species seems to be allied most closely to B. vigilans, 

 differing from it chiefly in the slight elevation of its ocular tubercle. 

 It constitutes, indeed, a very inconspicuous feature in this species, 

 while in B. vigilans it is a very prominent one. The proportion of 

 height and length is different, the height being relatively greater. 

 Finally the posterior outline is much more broadly rounded. 



Occurrence. — Middle Cambrian (Menevian): St. Davids, Wales. 



Genus WALCOTTELLA, new genus 



Carapace bivalved, subovate, 3 to 7 mm. in length, hinge straight, 

 rather long. Valves moderately convex, usually with a more or less 

 prominent, conical eminence situated in the median third of the length 

 and occasionally one or two much less conspicuous nodes near the 

 antero-dorsal angle. Edges of valves thin, bordered, gaping anteriorly 

 and posteriorly. Test phosphatic, thin, pliable, closely punctate 

 exteriorly. 



Genotype. — Walcottella apicalis, new species. 



This genus is named after the late Dr. Charles D. Walcott, to 

 whose acumen and diligence science is indebted for the splendid col- 

 lection of Cambrian fossils in the United States National Museum. 

 All of the species so far known of this genus were procured by him 

 from the late Middle Cambrian Bright Angel shale in the Grand 

 Canyon of the Colorado in Arizona. 



The thirteen species brought together under the above generic 

 designation, though exhibiting a considerable range of variation, 

 seem yet to constitute a natural association. The most variable 

 and at the same time the most obvious of the generic characters is 

 the submedian eminence. In W. apicalis and W. concentrica it is situ- 

 ated very near the center of the valves. In W. hreviuscula, according 

 to the adopted orientation of the valves, this eminence is well behind 

 the middle, but in all of the remaining species it tends to move 



