B 



PATERINID^. 357 



Ohservations. — This form recalls Micromitra (Paierina) labradorica (Billings), which is found 

 in association with Discinella at Bio, Canada. The size and character of the shell indicate its 

 relationslxip to Micromitra rather than to Kutorgina. 



Formation and locality. — Lower Cambrian: With Discinella in drift blocks of glauconitic quartzitic sand- 

 stone at the following localities [Moberg, 1892b, pp. 112 and 115]; (310f) west of Ekerum; (390a) at several points 

 near Stora Ror; (390(i) north of Rohalla; and (390h) on Nordmannaskar Island; all in the Kalmar district of the 

 Geological Survey of Sweden, Oeland Island, Sweden. 



Moberg [1892b, p. 114] describes some fragments which he refers to Kutorgina sp. From 

 his statement that tlie fragments appear to be of a horny texture it is highly probable that 

 thej^ belong to the genus Micromitra. 



Micromitra (Paterin.4.) wapta Walcott. 



U 



Text figures 29A-B. 



Mcromtim (Po«€rma) tyapia Walcott, 1908, Smithsonian Misc. Coll., vol. 53, No. 3, p. 59, PI. VII, fig. 6. (Described 

 and discussed as below as a new species. Fig. 6 is copied in this monograph as fig. 29A.) 



Shell large and thick for a species of this genus. Ventral valve depressed, conical, with 

 the apex above a narrow false area that is outlined by the abrupt curvature of the shell. As 

 the shells usually occur compressed in the siliceous shale, 

 the false area is concealed and the posterior slopes from 

 the apex form a blunt angle at the apex. Dorsal valve 

 transverse, moderately convex, with the posterior margin 

 nearly straight and a little shorter thaii the greatest 

 width of the valve ; beak small, marginal ; cardinal slope 

 and false area unknown. 



Surface marked by concentric, slightly irregular, ^ 



rounded lines and ridges of growth that are grouped in ^^^^^ 29.- Micromitra (Paicrina) wapta waicott. a, 



bands of varying width; a few radiating striae or lines E.x-tenor of ventral valve, the type specimen (U.S. Nat. 



occur on the central portions of one ventral valve; with ItMu.'StNfL^i.r'"™"'""''''™'™ *''■'■ 



a lens magnifying 20 diameters an occasional roughness ^he specimens represented are from Locality 35c, a 



can be seen in reflected light on the surface of some of drift Wock of Lower Cambrian shale on Mount Bosworth, 

 .1 j_ ■ • ^ Britisli Columbia. Figure 29.\ Is copied from Walcott 



the concentric ridges. _ _ _ [i908d,pi.vn,fig.6i. 



Observations. — This is one of the largest species of 

 the genus. One ventral valve has a length and breadth of 14 mm.; several are 9 to 11 mm. in 

 diameter. It compares in size with Micromitra (IpJiidella) nyssa, from the same geologic hori- 

 zon in Montana, but the latter has a reticulate exterior surface of the J/. (/.) pannula type. It 

 was at first thought that this species might be the old shells of Acrothele colleni Walcott, but 

 a careful comparison with the younger stages of growth of M. (P.) wapta shows that the latter 

 has only very indefinite traces of the highly ornate surface of Acrotliele colleni and that the 

 apex of the ventral valve of M. (P.) wapta is imperforate and over the posterior margin and not 

 on the general surface of the valve in advance of the margin, as in Acrothele colleni. The two 

 species were found associated on Mount Bosworth. M. (P.) wapta is of the same type as M. 

 (P.) labradorica, M. (P.) prospectensis, and M. (P.) stissingensis. It differs from all in having 

 more irregular, less definite threadlike concentric lines, and in the manner in which the strise 

 are assembled in ridges. 



The specific name is derived from Lake Wapta, which lies a little to the west of the type 

 localit}^. 



Formation and locality. — Lower Cambrian : (35c) Drift blocks of siliceous shale supposed to have come from the 

 Mount Whyte formatioti [Walcott, 1908f, p. 214], found on the south slope of Mount Bosworth, a short distance northwest of 

 the Canadian Pacific Railway track between Stephen a?id Hector, eastern British Columbia, Canada. 



(35e) About 270 feet (82.3 m.) below the Middle Cambrian, in a greenish siliceous shale correlated with No. 3 of 

 the Mount WTiyte formation on Mount Bosworth [Walcott, 1908f, p. 214], in the amphitheater between Popes Peak 

 and Mount W^hyte, about 3 miles (4.8 km.) northwest of Lake Louise, southwest of Laggan on the Canadian Pacific 

 Railway, Alberta, Canada. 



