OBOLIDiE. 389 



Cambrian. This may be seen by comparing with figures of Lingulella hayesi (Walcott) (PI. XXV) 

 of the Middle Cambrian and Lingulella radula Matthew (PI. XLV) of the Upper Cambrian. 



Ololus cyane is of the same tj^pe as Lingulella iole (Billings) and is associated with it 

 in a horizon that appears to correspond with the upper portion of the Chazy and base of the 

 Trenton of the New York section. It differs in being more cuneate and less elongate. 



Formation and locality. — Lower Ordovician: (314d.) Limestone of Division P [Billings, 1865a, p. 216] of the 

 "Quebec group," 4 miles (6.4 km.) northeast of Portland Creek, Newfoundland. 



Obolus discoideus (Hall and Whitfield). 

 y 



Plate XVIII, figures 6, 6a-d. 



Oholella discoida Hall and Whitfield, 1877, U. S. Geol. Expl. 40th Par., vol. 4, p; 205, PI. I, figs. 1 and 2. (Described. 



One of Hall and WTiitfield's specimens, likely the one represented by fig. 2, is redraw^ in this monograph, PI. 



XVIII, fig. 6c; the specimen represented by fig. 1 is not figured in this monograph.) 

 Oholella discoidea Hall and Whitfield, Walcott, 1884, Mon. U. S. Geol. Survey, vol. 8, p. 14. (New localities mentioned.) 

 Oholella f discoidea Hall and Whitfield, Walcott, 1886, Bull. U. S. Geol. Survey No. 30, p. 111. (Questions generic 



reference.) 

 Oholella ? discoidea Hall and Whitfield, Hall and Clarke, 1892, Nat. Hist. New York, Paleontology, vol, 8, pt. 1, p. 69. 



(Questions generic reference.) 

 Oholus {Lingulella) discoideus (Hall and Whitfield), Walcott, 1901, Proc. U. S. Nat. Mus., vol. 23, p. 673. (Merely 



changes generic reference.) 



General form broad ovate to subcircular, with the ventral valve obtusely acuminate and 

 the dorsal valve more broadly rounded posteriorly; both valves depressed convex, the umbo 

 of the ventral valve rising slightly toward the posterior margin. Surface of shell marked by 

 very fine, concentric undulating strise and lines of growth. When partly exfoliated the 

 inner lamellose layers are imbricated, their outer edges being irregular. The only traces of 

 the interiors observed show fine concentric striae of growth. Shell of medium thickness. It is 

 built up of a very thin outer layer and numerous inner layers arranged more or less obliquely 

 to the outer layer over the frontal portions. The largest valve has a length of 4.25 mm. with a 

 width of 4 mm. No interiors of either valve have been found among a large number of specimens. 



Observations. — This pretty little shell is certainly not an Oholella. In shell structure and 

 form it is like Obolus. 



Formation and locality. — Lower Ordovician : (185z) Limestones at the base of the Lower Ordovician [Walcott, 

 1908t, p. 191], in Blacksmith Fork Canyon, about 9 miles (14.4 km.) east of Hyrum, Cache County, Utah. 



tipper Cambrian: (313j [Hall and Whitfield, 1877, p. 305]) Limestone in the Eureka district; (66) Dunderberg shale 

 [Walcott, 1908f, p. 184], on the first ridge north of the Dunderberg mine; (62) limestone in the Dunderberg shale 

 [see Walcott, 190Sf, p. 184], in canyon immediately north of Adams Hill; and (64) limestone near the Bullwhacker 

 mine; all in the Eureka district [Hague, 1892, Atlas], Eureka County, Nevada. 



(8f) Limestones at summit of canyon, 10 miles (16.1 km.) south of Egan Canyon, east side of Egan Range, White 

 Pine County, Nevada. 



(54e) About 200 feet (61 m.) above the Middle Cambrian and 1,025 feet (212.4 m.) below the top of the Upper 

 Cambrian, in limestones forming 3 of the St. Charles formation; and (54f) about 150 feet (45.7 m.) above the Middle 

 Cambrian and 1,075 feet (327.7 m.) below the top of the Upper Cambrian in the light-gray sandstone forming 4 of the 

 St. Charles formation; both in Blacksmith Fork Canyon [Walcott, 1908f, p. 193], about 10 miles (16.1 km.) east of 

 Hyrum, Cache County, Utah. 



(56g) Limestone of the St. Charles formation [Walcott, 1908a, p. 6], in the valley of the stream which flows into 

 Mill Canyon from the west, about 6 miles (9.6 km.) west-southwest of Liberty, and 15 miles (24.2 km.) west of Mont- 

 pelier. Bear Lake County, Idaho. 



(151) Limestone in point overlooking Chum Canyon, on the west side of the Bridger Range, Gallatin County, 

 Montana. 



Middle Cambrian: (58) Shaly limestone in upper beds of Secret Canyon shale, east side of New York and Secret 

 canyons, Eureka district [Hague, 1892, Atlas], Eureka County, Nevada. 



Specimens that are somewhat doubtfully referred to this species occur at the following 

 locality : 



Upper Cambrian : (302r) About 1,000 feet (305 m.) above the quartzitic sandstones in the " Yogo limestone (Devono- 

 Silurian)" of W. H. Emmons [1907, p. 34], near Princeton, Philipsburg quadrangle (U. S. Geol. Survey), Granite 

 County, Montana. 



