68 SMITHSONIAN MISCELIvANEOUS COLLECTIONS VOL. 53 



they are in the form of sharp, finely zigzag, transverse stri?e much 

 Hke the shells from the Big Horn Mountains of Wyoming. This 

 surface is formed by the interruption of very fine, sharp ridges that 

 curve from the umbo outward toward the sides and front of the shell 

 like engine-turning striae on a watch-case. 



Formation and Locality. — Middle Cambrian : Shales about 400 

 feet (122 m.) above the quartzitic sandstones, from high peak south- 

 west of Lookout Pass, Onaqui Range, west of Vernon, Tooele 

 County, Utah. 



OBOLUS (WESTONIA) ELONGATUS, new species 



Plate 7, Figure 12 



General form elongate oval, with the ventral valve acuminate and 

 the dorsal valve elongate oval. Convexity unknown, as the shells 

 are all flattened by compression. 



The outer surface is marked by fine concentric lines of growth 

 crossed by a series of finely denticulated, imbricating lines that start 

 on each cardinal slope and extend obliquely forward across the 

 median line, and then curve out toward the sides of the shell ; minute 

 rhomboidal spaces are formed over the posterior and central portions 

 of the shell by the crossing of the oblique lines ; the denticulated 

 margin faces forward and is seen only on the thin epidermal layer, 

 while the general system of oblique lines shows on both the outer 

 layer and the next inner layer of the shell. 



The shell is built up of several thin layers or lamellse. The 

 largest specimen of the ventral valve has a length of 9 mm. ; width, 

 5 mm. ; a dorsal valve 6 mm. long has a width of 4 mm. Nothing 

 is known of the interior of these valves. 



This is a more elongate species than O. (W.) bottnica (Wiman) 

 [1902, p. 51] and O. (W.) Unlandensis (Walcott) [1902, p. 611]. 

 The oblique surface lines have 'the same general direction as those 

 of the latter species, but they are finely denticulated on their front 

 margin and cross at the center at a greater angle. 



Formation and Locality. — Middle Ordovician : Gray, siliceous 

 shales just below a band of quartzitic sandstones, probably corre- 

 sponding in position to the upper part of the Simpson formation of 

 the Oklahoma section; Wasatch Canyon, 5 miles (8.05 km.) north of 

 Brigham, Box Elder County, Utah. 



