NO. II NEW UnVER CAMBRIAN SUBFAUNA 3II 



The largest shell in the collection has a diameter of 46 mm. ( pi. 5 1, 



fig- 4)- 



Specimens of the shell are abundant as casts and impressions in the 

 siliceous shale. The original shell has disappeared, but from what we 

 know of the shell of Mickivit::.ia inonUifcra, it was probably formed of 

 calcivun phosphate. 



One other American species of Alickzvitcia is known, il/. occidcns 

 Walcott.^ The punctate surface is much like that of M. muralciisis, 

 but the form as far as known is not similiar. 



Formation and locality. — Lower Cambrian : (6ik) Mahto forma- 

 tion ; dark, hard siliceous shale ; northeast base of Mumm Peak above 

 ]\Iural Glacier on west side of Hitka.Pass, 6 miles (9.6 km.) in a 

 direct line north of the summit of Robson Peak and northwest of 

 Yellowhead Pass, in western Alberta, Canada. 



LINGULELLA CHAPA, new .species 

 Plate 50, figs. 4-9 



In form this species is not unlike Lingulella schuchcrti (Walcott)"^ 

 from the Lower Cambrian of New York. It differs in having a more 

 acuminate ventral valve, and possibly in other details not shown by 

 the rather poor specimens of L. schucherti. Several species of 

 Lingulella from the Upper Cambrian have nearly the same outline 

 of the valves as those of L. chapa, notably L. randomensis f Walcott)^ 

 and L. mosia osceola (Walcott).'* Comparison may also be made with 

 the broader forms of L. perattenuata (Whitfield).' Linguella chapa 

 is distinguished by the very strong vascular canals of the ventral valve 

 (fig. 6) and the shallow median sinus of the dorsal valve (figs. 4, 8, 

 and 9) . 



The average length of the ventral valve is from 6 to 7 mm. The 

 dorsal valve is about one-sixth shorter than the ventral. 



Specimens of this species occur in such large numbers on partings 

 in the shale as nearly to cover the surface, or they may be scattered 

 about among other brachiopods and fragments of trilobites. 



The specific name is taken from Chapa (beaver), the name of the 

 high point at the foot of Mural Glacier where the first specimens of 

 this species were found in a block of shale lying on the glacier. 



^ Alonogr. U. S. Geol. Survey, Vol. 51, 1912, p. 3JI, pi. 6, fig. 4. 

 'Idem, pi. 21, fig. 6. 

 ''Idem, pi. 21, figs. 5, Sa. 

 * Idem, pi. iS, figs. 2, 2a-c. 

 ^Idem, pi. 21, figs. ic-d. 



