OBOLIDiE 479 



and in a slightly different character ot limestone is illustrated and provisionally referred to the 

 same species (PL XXIV, fig. 5a). 



In outline this shell resembles Lingulella beUa (Walcott) and L. bellula (Walcott) from 

 Newfoundland; it is more broadly acuminate than these species and much smaller than 

 Lingulella hella. It may also be compared with L. punctata (Walcott), from which it differs in 

 being more ovate. 



Formation AND LocAiiTY. — Upper Cambrian: (313f) Limestone at Schellbourne, Schell Creek Range, White Pine 

 County, Nevada. 



Middle Cambrian: (3e) Thin-bedded limestone less than 400 feet (121.9 m.) above the quartzitic sandstones of 

 the Cambrian, near Ophir, Oquirrh Range, Tooele County, Utah. 



(llw) About 1,050 feet (320 m.) above the Lower Cambrian and 3,350 feet (1,021.1 m.) below the Upper Cambrian 

 in the shales forming Id of the Swasey formation [Walcott, 1908f, p. 182], at the head of Dome Canyon; (3w) about 

 2,350 feet (716.3 m.) above the Lower Cambrian, and 2,050 feet (624.8 m.) below the Upper Cambrian, in the central 

 portion of the thin-bedded limestones forming Ic of the Marjum limestone [Walcott, 1908f, p. 180], in the cliff about 

 2 miles (3.2 km.) southeast of Marjum Pass; (lOy) about 2,900 feet (884 m.) above the Lower Cambrian and 1,500 feet 

 (457.2 m.) below the Upper Cambrian in the central portion of the limestone forming la of the Marjum limestone 

 [Walcott, 1908f, p. 179], about 1 mile (1.6 km.) south-southwest of Marjum Pass; (3x and Hx) about 2,200 feet (670.6 m.) 

 above the Lower Cambrian and 2,200 feet (670.6 m.) below the Upper Cambrian, in the limestones forming Id of the 

 Marjum limestone fWalcott, 1908f, p. 180], 2.5 miles (4 km.) east of Antelope Springs, in ridge east of \\Tieeler Amphi- 

 theater; and (llq and lly) about 2,350 feet (716.3 m.) above the Lower Cambrian and 2,050 feet (624.8 m.) below the 

 Upper Cambrian, in the limestones forming Ic of the Marjum limestone [Walcott, 1908f, p. 180], 2.5 miles (4 km.) east 

 of Antelope Springs, in ridge east of Wheeler Amphitheater; all in the House Range [Walcott, 1908f, Pis. XIII and 

 XV], Millard County, Utah. 



(14m) Limestone about 7 miles (11.2 km.) south ot Towner's ranch, Indian Creek, Lincoln County; (54) Eldo- 

 rado limestone [Walcott, 1908f, p. 184], on the east slope of Prospect Mountain, in New York Canyon, Eureka district 

 [Hague, 1892, Atlas], Eureka County; (59) limestone at the base of the western slope of Combs Peak, near the plain 

 of Antelope Valley, Eureka district [Hague, 1892, Atlas], Eureka County; and (313e) limestone 2 miles (3.2 km.) 

 west of Green's ranch, ^Vhite Pine County; all in Nevada. 



A shell which is provisionally referred to Lingulella arguta occurs associated with the latter 

 species in the following locality: 



Middle Cambrian : (313a) Limestone at Schellbourne, Schell Creek Range, White Pine County, Nevada. 



Lingulella atava (IVIatthew). 



Plate XXXV, figures 5, 5a-h. 



Leptobolus atavus Matthew, 1899, Bull. Nat. Hist. Soc. New Brunswick, vol. 4, pt. 3, No. 18, pp. 200-201, PL II, 



figs, la-b and d-f. (Described and discussed as a new species. The specimens represented by figs, la and Id 



are redrawn in this monograph, PI. XXXV, figs. 5 and 5c, respectively.) 

 Obolus (Lingulepis) gregioa Walcott (in part) [not (Matthew)], 1901, Proc. U. S. Nat. Mus., vol. 23, pp. 692 and 694. 



(Matthew's "Leptobolus atavus" mentioned as the young of "Lingulepis gregiva.") 

 Obolus (Lingulella) atavus (Matthew), Walcott, 1902, Proc. U. S. Nat. Mus., vol. 25, pp. 609-610. (Described and 



discussed essentially as below.) 

 Leptobolus atavus Matthew, 1903, Geol. Survey Canada, Rept. Cambrian Rocks Cape Breton, pp. 106-109, PI. VI, 



figs. 2a-b and d-g. (Described and discussed. Pigs. 2a-b, d-e, and g are copied from Matthew, 1899b, PI. II, 



figs, la-b and d-f, respectively.) 



General form elliptical, with the ventral valve subacuminate, and the dorsal valve broadly 

 subacuminate in outline. In the shorter form of the valves the sides are almost uniformly 

 rounded from the cardinal slopes to the frontal margin. The convexity of the valves is fairly 

 strong, that of the dorsal valve being broken by a slight longitudinal flattening that extends 

 from the posterior portion to the frontal margin. As shown by the matrix, the outer surface 

 is marked by concentric ridges and fine striae of growth. The interior cast shows concentric 

 lines and traces of rather coarse radiating lines. None of the specimens preserve the shell, 

 but from the strength of the interior surface markings it is inferred that the shell was rather 

 thick. 



The longest ventral valve in the collection has a length of 6 mm.; width, 3. .5 mm. The 

 dorsal valves are slightly shorter. 



The area of the ventral valve is divided at the center by a strong pedicle furrow, and 

 about midway between the pedicle furrow and the outer margin by clearly marked flexure 



