56 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 78 



sharply defined, rather narrow, apparently double, with an extremely 

 delicate accessory flange on its outer edge. Surface of shell appearing 

 smooth and polished, minutely punctate when magnified about 15 

 diameters. 



Dimensions of type, a right valve: Length 1.1 mm., height about 

 0.8 mm., depth about 0.26 mm. 



Remarks. — The original type and only known specimen of this 

 species seems in an excellent state of preservation. The only possible 

 exception to this condition is found in the dentlike depressions of the 

 surface. These look too much like accidental indentations of the 

 pliable shell to be accepted unqualifiedly without the corroborative 

 evidence of other specimens. That there is good ground for suspicion 

 is shown by a specimen of A. woodi having similar indentations but 

 still recognizable by the characteristic loop of that species. Should 

 they prove normal structures, they would aft'ord unusually striking 1 

 criteria in the determination of the species. If, on the other hand, 

 they could be shown to be abnormal, it would practically eliminate 

 all differences of any consequence between A. stereope and A. enyo. 

 However, until the validity of the differences on which the separation 

 of the two species is based can be determined, they should be recog- 

 nized as distinct. 



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

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

 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.—C&t. No. 56498, U.S.N.M. 



ALUTA WOODI (Walcott) 



Plate 8, Figures 7, 8 



Bradoria woodi Walcott, Proc. U. S. Nat. Mus., vol. 29, 1905, p. 102. 

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

 p. 227, pi. 23, fig. 15. 



Description. — Outline of carapace obliquely acuminate-ovate, 

 truncated along the hinge line, rather broadly rounded behind and 

 below, the anterior side oblique, straight or slightly concave and 

 drawn out somewhat bealdike at the anterior extremity of the hinge; 

 postdorsal angle rather well defined, the hinge line and upper part of 

 posterior margin making an angle of about 120°. Marginal rim 

 distinct, of moderate width. Surface of valves rather strongly 

 convex in the middle and posterior parts, depressed on either side of 

 a low, mid-dorsal elevation. The principal characteristic is a thin, 

 curved ridge, beginning at the anterior extremity and extending 

 obliquely backward and downward to a point consideraly behind tjie 

 center of the valve. Here it turns on itself and forms a loop inclosing 

 a large median relatively depressed elliptical space. Two small nodes 



