526 CAMBKIAN BRACHIOPODA. 



surface of the inner layer is marked by very fine radiating striae, also concentric lines of growth. 

 The shell is below the average thickness and is formed of a thin outer layer and one or more 

 inner layers or lamellae. 



The largest ventral valve has a length of 15 mm.; width, 11 mm. As shown by a partial 

 cast the area is of medium length, and divided midway by a narrow, strongly marked cast of 

 the pedicle furrow. 



Observations. — In form the valves of this species somewhat resemble those of Lingulella 

 ampla (Owen) (PI. XXVIII), and more closely those of L. isse (Walcott) (PI. XXXIX). In 

 the absence of all interior markings no further comparisons can be made. 



The species derives its specific name from its occurrence in the Pogonip limestone. 



Formation and locality. — Passage beds l^etween the Upper Cambrian and the Ordovician: (801) Arenaceous 

 Pogonip limestone, on east slope of ridge east of Hamburg Ridge; (205) siliceous limestone on Roundtop Mountain; 

 (203a) limestones at base of Pogonip limestone, in the spur on Hamburg Ridge extending out southwest from Wood 

 Cone; and (211) siliceous Pogonip limestone, on spur of Hamburg Ridge extending southwest fi'om Wood Cone; all 

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



Specimens somewhat doubtfully referred to this species occur at the following localities: 

 ITpper Cambrian: (32f) Thin-bedded siliceous limestones near the top of the Upper Cambrian, about 2 miles 



(3.2 km.) southeast of Muskrat Spring, on the northwest face of Grantsville Peak, Stansbury Range, Tooele County, 



Utah, 



TTpper? Cambrian: (358a) Siliceous limestone in Pinal County, Arizona. 



Lingulella prima (Conrad MS.) (Hall). 



Plate XXVII, figm-es 1, la-c, 



Lingula ovata Emmons [not McCoy], 1842, Nat. Hist. New York, Geology, pt. 2, p. 105. (Mentioned.) 



lAngula prima (Conead MS.) Hall, 1847, Nat. Hist. New York, Paleontology, vol. 1, p. 3, PL I, fig. 2. (Described 



and discussed. It is the first description of the fossil, though no reference is made to the fact that it is a new 



species.) 

 I/ingula prima Hall, Emmons, 1855, American Geology, vol. 1, pt. 2, p. 202. (Described.) 

 Lingulepis privia (Hall), Miller, 1877, American Paleozoic Fossils, Catalogue, p. 115. (Merely changes generic 



reference.) 

 Obolella prima (Hall), Whitfield, 1884, Bull. Am. Mus. Nat. Hist., vol. 1, No. 5, pp. 142-143, PI. XIV, figs. 3-5. 



(Discussed.) 

 Lingulella f prima (Hall), Hall and Clarke, 1892, Nat. Hist. New York, Paleontology, vol. 8, pt. 1, p. 69, footnote. 



(Discussed.) 

 Lingulepis prima (Hall), Schuchert (in part), 1897, Bull. U. S. Geol. Survey No. 87, p. 260. (Merely changes generic 



reference. Includes species other than Hall's "Lingula prima.") 

 Obolus (Lingulepis) primus (Hall), Walcott, 1901, Proc. U. S. Nat. Mus., vol. 23, p. 673. (Merely changes generic 



reference.) 



General form subovate with the ventral valve subacuminate and the dorsal valve broadly 

 subacuminate. There is a tendency in some individuals to a subcuneate outline. Valves 

 moderately convex, increasing in some shells to almost strongly convex. There is some range 

 of variation in the outlines of the valves, as shown by Plate XXVII, figures 1 and la. The 

 surface of the shell is marked by concentric lines and small undulations of growth and by very 

 fine radiating striae. Wlien the outer layer is exfoliated the inner layer is seen to be marked 

 by sharp radiating striae and a few CQncentric lines of growth. The interior surface shows 

 fine radiating striae and a few scattered pits. The shell is of medium thickness and formed 

 of a thin outer layer and several inner layers, or lamellae, which are more or less oblique to the 

 outer layer; the lamellae are much more numerous toward the margins and form a rather thick 

 rim around the anterior and anterolateral margins. The average length of the ventral valve 

 is 5 mm., width 4 mm. The dorsal valve is slightly shorter in proportion to its width. 



As shown in the interior casts the area of the ventral valve is relatively short; it is divided 

 at the center by a rather strongly marked pedicle furrow and well out toward its margins by 

 clearly defined flexure lines. Faint traces of striae of growth cross the area parallel with its 

 base; the area of the dorsal is not shown in any of the specimens in the collection. 



The cast of the interior of the ventral valve shows the visceral cavity (v), the trapezoidal 

 area (c), and the rather strong median ridge, which extends from the area forward to the anterior 



