4 PROCEEDINGS OP THE NATION AL MUSEUM vol. 79 : art. 33 



Beckwithia departs more widely from the other merostomes, since 

 in the new form the phite from which the telson spine arises is as 

 large as and similar to the pygidium of a large-tailed trilobite, while 

 in Aglaspis the pygidial plate is relatively small and triangular. 

 No trace of segmentation of this large telson plate is visible under 

 a lens. 



Beckwithia recalls Strdbops ^ in the absence of longitudinal loba- 

 tion, but the pustulose test, the more central position of the eyes, 

 the presence of genal spines and, above all, the 8 instead of 12 ab- 

 dominal segments, and finally the large pygidial plate instead of the 

 spiniform telson serve to distinguish it at once. 



Raasch states that the texture of Beckwithia resembles that of 

 fragments occurring in the lower Eau Claire formation and sug- 

 gests that, in view of the extremely early Upper Cambrian age of 

 those remains, they might represent the new genus. 



No confusion with Sidneyia is possible, and Amiella is so incom- 

 pletely preserved that comparisons with it are not profitable. The 

 absence of longitudinal trilobation serves to distinguish Beckwithia 

 from all the other Burgess shale merostome genera. 



Formation and locality. — Middle Cambrian, Marjum formation; 

 Weeks Canyon, House Range, Utah. 



^oZo^ype.— U.S.N.M. No. 8-4170. 



OBOLUS JOHNI, new species 



Plate 1, FiGtnREs 1, 2 



Five brachiopods are attached to the dorsal surface of Beckiuithia 

 typa and about a dozen other, chiefly fragmentary, specimens occur 

 in the matrix. This association is likely merely commensal. 

 From the fact that these brachiopods efface the surface features, it 

 would seem that they lived for a long time on this particular test, 

 and were not merely compressed on the shell during fossilization. 



C oinparison. — This species of OhuJus compares fairly closely with 

 O. Tiicconnelli pelias Walcott ^ from the Neolenus zone of the Mar- 

 jum formation, in Wheeler Amphitheatre, which is a few miles 

 north of Weeks Canyon. The new species differs in its broader 

 shape, which results in a somewhat rounder outline. It is also con- 

 siderably smaller. Its posterior outline is also more circular, lack- 

 ing the flattening of the described species. 



The specific name is given in recognition of the work of Emory J. 

 John, who gives much time to collecting in the desert ranges of Utah. 



Formation and locality. — Middle Cambrian, Marjum formation; 

 Weeks Canyon, House Range, Utah. 



Gotypes.—U.S.'^.M. No. 84171, on Beckwithia typa No. 84170. 



8 Beecher, Amer. Journ. Sci., vol. 12, p. 364, pi. 7, 1901. 

 ' Mon. U. S. Geol. Suiv. 51, p. 398, pi. 23, figs. 3b, 3c, 1912. 



o 



