AET. 4 CAMBRIAN CONCHOSTRACA — ULRICH AND BASSLER 57 



occur on this ridge, one at the anterior end of the loop, the other larger 

 and somewhat crescentic in shape, about midway between the middle 

 of the valve and the anterior extremity of the hinge. Surface very 

 mmutely punctate under a strong lens. 



Dimensions of original type, a left valve: Length 2.0 mm., height 

 1.25 mm., depth about 0.5 mm. 



Remarks. — The specimen used by Walcott in describing this species 

 is in an unusually good state of preservation. The outline differs 

 somewhat from that of all other species referred to the genus, but the 

 principal and most striking peculiarity is the long curved ridge which 

 traverses the anterior and middle parts of the valve. A second 

 specimen, discovered in the course of these studies, and satisfactorily 

 identified with this species by its outline and the presence of the looped 

 ridge, has several indentations of the surface that are entirely absent 

 in the type specimen. These indentations are comparable with those 

 marldng the surface of A. stereope and being clearly abnormal in the 

 case of A. woodi, strongly suggest a similar origin for the other as well. 



Occurrence. — Middle Cambrian; a fine-grained, bluish-black lime- 

 stone bowlder believed to have come from the lower part of the 

 Ki-sin-ling limestone, collected in river drift 1 mile south of Chon- 

 p'ing-hien, on the Nan-kiang River, southern Shensi, China. 



Holotype.—Csit. No. 56494, U.S.N.M. 



ALUTA FRAGIUS (Walcott) 



Plate 8, Figure 2 



Bradoria fragilis Walcott, Proc. U. S. Nat. Mus., vol. 29, 1905, p. 100. 

 Alula fragilis Walcott, Research in China, Carnegie Institution, vol. 3, 1913, 

 p. 226, pi. 23, fig. 13. 



Original description. — "Hinge line nearly straight, about one-fifth 

 shorter than the width of the valve. Posterior cardinal angle obtuse, 

 with the marginal curve long and passing into the broad curve of the 

 lower end of the valve; anterior cardinal angle about 75°, with the 

 anterior margin nearly straight to where it merges into broad curve 

 of the lower part of the valve. 



"Surface of the valve wrinkled to such an extent that it looks like 

 wrinkled parchment. What may be an ocular tubercle occurs a short 

 distance from the hinge and anterior margin. Surface minutely 

 punctate under a strong lens. 



"Width [length], 2.25 mm.; length [height], 2 mm.; depth unknown, 

 as the flexible test has been compressed." 



Remarks.— The type of this species is so badly crushed that satis- 

 factory comparisons with the other species can not be made. The out- 

 line even may not be exactly preserved. Assuming that it is nearly 

 normal in the type specimen, the outline may be described as essen- 

 tially like that of A. woodi and A. eris. Similarly crushed carapaces 



