66 PROCEEDINGS OF THE NATIONAL MUSEUM vot. 78 



POLYPHYMA LAPWORTHI Groom 



Plate 8, Figures 26, 27 



Polyphyma lapworthi Groom, Quart. Journ. Geol. Soc. London, vol. 58, p. 84, 

 pi. 3, figs. 1-8. 



This species, the genotype of Polyphyma, is fully described and 

 illustrated by Groom, so that it is only necessary to point out its 

 chief characteristics as indicated by him and as shown in the repro- 

 ductions of his original figures on Plate 8. These are a subcentral 

 parallel direct reniform elevation, three tubercles near the dorsal 

 margin and an anterior sub triangular lobe. 



Occurrence.- — Lowest black shales (Cambrian): Southern Malverns, 

 England. 



POLYPHYMA MARGINATA, new species 



Plate 8, Figures 28, 29 



Description. — Valves semicircular, the height shghtly greater than 

 half the length of the hinge line. Surface now rather depressed 

 convex, originally probably ventricose, with 10 to 12 partly con- 

 fluent rounded nodes separated by narrower depressed spaces. 

 Eight of these are small and in part inconspicuous and arranged 

 closely along the dorsal and posterior margins, while a low ridge 

 parallels the front border. Two much larger nodes, both somewhat 

 crushed in the best specimen, occupy the middle part of the ventral 

 half. The hinder of these two elevations is low and broad based, the 

 forward one a Uttle smaller at the base but rising to a much greater 

 height; whether rounded at the summit or conical can not be deter- 

 mined. A narrow, sharply defined rim forms the extreme edge on 

 the anterior ventral and dorsal sides. Within this the best specimens 

 exhibit two distinct parallel folds, which become obsolete in the post- 

 ventral part and possibly were produced by compression of the 

 phable test. 



Dimensions of the largest and best specimen, the right valve 

 figured on Plate 8: Length of hinge Une about 3.2 mm., greatest 

 height 2.0 mm. 



Occurrence. — In black shales classified as upper Cambrian by 

 Doctor Walcott, west side of Manuel's River, Conception Bay, 

 Newfoundland. 



Holoty pe.—C^t. No. 56492, U.S.N.M. 



Remarks .—Th.e half dozen or more specimens of this species in 

 the National Museum collection have been subjected to more or less 

 compression; and as they lie variously with respect to its direction, 

 they exhibit a corresponding variety of distortion. Thus, when they 

 lie so that the length is reduced to about haK, the nodes seem to 

 arrange themselves in four irregularly undulating vertical ridges. 

 But as each specimen looks different from the others, it is useless 



