54 PROCEEDINGS OF THE NATIONAL MUSELTM vol. 78 



the length of valve, straight, forming an angle of about 80° with the 

 nearly straight anterior edge; postdorsal angle obtuse. Surface 

 moderately convex, with an ill-defined, broad depression in front of 

 the middle of the dorsal slope and three nodelike elevations about it. 

 The largest and roundest of the nodes is located at the base of the 

 depression and somewhat nearer the antero-ventral edge of the valve 

 than the middle of the dorsal edge. A thin ridge extends from this 

 node toward the antero-dorsal angle and about midway between 

 the two points the specimen shows part of the base of the second node 

 rising from the ridge. Dorsal parts of specimen imperfect but show- 

 ing the remains of a third small elevation near the middle of the 

 dorsal edge. Marginal rim sharply defined, thick and convex on the 

 anterior side, much thinner and comparatively indistinct (perhaps 

 imperfect) on the posterior side. Under a strong lens the surface of 

 the test is covered with shallow punctae. 



Dimensions of a right valve: Length about 2 mm., height about 

 1.5 mm., depth about 0.5 mm. 



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

 species has been slightly crushed and is imperfect in its dorsal and 

 posterior parts. Judging from what may be seen, the species appears 

 to be closely related to the associated A. enyo (Walcott) and A. ivoodi 

 (Walcott). In the former the anterior edge is more nearly vertical, 

 and the anterior half on the whole wider. A more important dif- 

 ference perhaps is that A. enyo is without the node at the base of the 

 dorsal depression. In A. woodi all three nodes are indicated, but the 

 anterior one and the lower one are both less developed, while the 

 thin ridge connecting them is prolonged posteriorly in a looplike 

 extension over the central part of the valve. 



Occurrence. — Middle Cambrian; compact, bluish-gray, thin-bedded 

 limestone; from shingle on gravel bar in the Lan Ho, 1 mile south of 

 Chen Ping Hsien, southeastern Shensi, China. 



Holotype.—C&i. No. 56496, U.S.N.M. 



ALUTA ENYO (Walcott) 



Plate 8, Figures 5, 6 



Bradoria enyo Walcott, Proc. U. S. Nat. Mus., vol. 29, 1905, p. 99. 

 Aluta enyo Walcott, Research in China, Carnegie Institution, vol. 3, 1913, p. 

 225, pi. 23, fig. 11. 



Description. — Carapace quadrangular, subovate, truncated along 

 the hinge line, broadly rounded on the posterior and ventral sides, 

 vertical at the front edge; antero-dorsal angle sharp, about 90°; 

 postdorsal angle more obtuse. Surface rather tumid in the posterior 

 two-thirds, depressed in the median part of the antero-dorsal quarter. 

 Principal (? ocular) node small, rounded, located slightly beneath 

 and in front of the middle of the antero-dorsal fourth. A double- 



