294 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 64 



southeast of the city of Helena. In the vicinity of the faults that 

 cut the shale the specimens are apt to be more distorted than from 

 the shales on Mount Helena. Rothpletz gives an excellent petro- 

 graphic description of the shale. In speaking of the subsequent 

 alteration of the shales he says, " Simultaneously with the origin of 

 the compression-bedding there occurred an inner movement in the 

 entire rock mass, which led in places to distortion, elsewhere to com- 

 pression. On this account the nearly circular fossil shells frequently 

 retain a lengthened form, and this is one of the difficult conditions in 

 the determination of the fossils." ^ 



The ventral valves of L. helena illustrated by Rothpletz (pi. 2, 

 figs. I, 2) are normal in form and size, but he does not name and 

 illustrate the dorsal valve except under other names. To me all of 

 his figures 4 to 12, plate 2, and figures 3 and 5, plate 3, are in size 

 and in such characters as are preserved, representatives of the dorsal 

 valves of L. iiclena (see pi. 44, figs. 1-5 of this paper). 



4. Obolclla crassa (Hall) (pi. 2, figs. 4, 5, 7-12, of Rothpletz). 



This is one of the greatest surprises of the Rothpletz determina- 

 tions. The shells illustrated are small, the largest according to Roth- 

 pletz 5 to 7 mm. in diameter, and the shell is preserved as phosphate 

 of lime. Obolclla crassa is a species with the valves from two to 

 three times the size of the shells figured by Rothpletz ^ and the valves 

 are thick and built up of layers of carbonate of lime, although 

 originally they may have been calcareo-corneous. All known speci- 

 mens of Obolclla crassa have been found in connection with the 

 Lower Cambrian Olcnellus fauna at localities on the eastern side of 

 the North American continent. 



To one acquainted with Obolclla crassa as the species occurs in the 

 limestones of the Straits of Belle Isle, Labrador, and the St. Lawrence 

 River province, it seems impossible to consider the distorted Park 

 shale specimens as even superficially related to Obolclla crassa or even 

 to the genus Obolclla. 



The Rothpletz figures referred to Obolclla appear to illustrate more 

 or less distorted dorsal valves of L. Helena. 



5. Obolclla atlantica Walcott (pi. 2, figs. 3 and 6, of Rothpletz). 

 Figure 3 appears to represent a fragment of ventral valve of 



Lingulella helena, and figure 6 a distorted dorsal valve. 



^ Rothpletz, p. 27, middle of last paragraph, going over to p. 28. 

 *Monogr. U. S. Geol. Surv., Vol. 51, 1912, pi. 54. 



