524 CAMBRIAN BRACHIOPODA. 



Lingulepis cuneolus Schucheet (in part) [not Whitfield], 1897, Bull. U. S. Geol. Survey No. 87, p. 259. (Merely 



refers Whitfield's Lingulepis perattenuatus to L. cuneolus.) 

 Obolus (Lingulella) perattenuatus (Wliitfield), Walcott, 1899, Mon. U. S. Geol. Survey, vol. 32, pt. 2, p. 443. (Merely 



changes generic reference.) 



The original description by Whitfield follows : 

 Shell spatulate or elongate-ovate, becoming acutely pointed toward the beak; sides below the middle 'of the 

 length of the ventral valve rounded; front margin very regularly curved; cardinal slopes straight, or sometimes slightly 

 convex; greatest width a little more than half the length of the ventral valve and sometimes nearly two-thirds as great. 

 Surface of the ventral valve depressed convex, very slightly subangular along the middle above the lower third of 

 the length, and a little more distinctly so in the upper part. Apex scarcely truncate. Dorsal valve considerably 

 shorter than the ventral, broadly truncated at the upper end, the line of truncation being distinctly arched. Surface 

 evenly convex. Structure of the surface of the shell polished, with fine, somewhat lamellose lines of growth. 



The material studied by Whitfield, now in the collections of the United States National 

 Museum, has been carefully worked over and the cardinal area of both valves developed in 

 the casts of the interior of the shell (PL XXI, figs. 1 and Id). The plane of the area of the 

 ventral valve coincides near its edges with the edge of the shell, but it rises quite rapidly toward 

 the pedicle furrow. It is divided at the center b}^ a rather deep, strongly marked pedicle 

 furrow and near the lateral margin by a rather sharp, very narrow flexure line (PI. XXI, figs. 

 la and Ic). The strife of growth cross the area parallel mth its base. They are sharp and 

 crowded on the lateral slopes, but are very indistinctly preserved in the pedicle groove. The 

 area of the dorsal valve is lower than that of the ventral and, in the typical specimens, shows 

 nothing more than the fine striae of growth (PI. XXI, fig. li). 



No traces of muscle scars or vascular markings have been found in the material from the 

 type locality in the Black Hills, but, in some casts of the interiors of valves from Texas, traces 

 of the visceral cavity and muscle scars are shown. In Plate XXI, figure le, the outline of the 

 visceral cavity (v) is preserved, also the main vascular sinus (vs). 



Both valves of the shell are much thiiiner than in Lingulella acutangula (Roemer). The 

 shell is formed of a thin outer layer and one or two inner layers or lamellse, which occur in the 

 posterior half of the shell. The surface of the outer layer is marked by concentric strise and 

 lines of growth and very fine, more or less interrupted radiating strise. The inner layer is 

 characterized on its outer surface by fine, concentric, radiating strise. A few minute punctse 

 occur on the inner surface of several shells, as shown by the papillse on the cast. 



Observations. — The most nearly related species in the American Cambrian rocks is L. 

 acutangula (Roemer). It differs in having a much thinner shell, and, as far as they are pre- 

 served, in the character and position of the interior markings and muscle scars. 



The type species was described from the "Potsdam formation" of the Black Hills. From 

 a recent study of the Black Hills Cambrian section I have found that it is from the Middle 

 Cambrian sandstones and limestones as they occur near the headwaters of Red Canyon Creek 

 and in the vicinity of Deadwood. It is also identified from the Middle Cambrian of central 

 Texas and in the same fauna from the "Tonto" sandstone of the Grand Canyon of the Colorado, 

 Arizona. In the Black Hills it is associated with Lingulella (Lingulepis) acuminata (Conrad) 

 and Dicellomus politus (Hall) . 



Formation and locality. — Upper Cambrian: (67c) Sandstone on Tatur Hill, 7 miles (11.2 km.) northwest of 

 Burnet, Burnet County; (70) limestone near Morgans Creek, Burnet County; and (68y) interbedded sandstone and 

 limestone on Packsaddle Mountain, Llano County; all in Texas. 



Middle Cambrian: (355) Sandstones on Red Canyon Creek, southwest side of Black Hills; and (365f) sandstones near 

 Deadwood, Black Hills; both in South Dakota. 



(74) Sandstone about 300 feet (91.4 m.) above the base of the Tonto group, at the head of Nunkoweap Valley; 

 and (74d) sandstone beds in the ' ' Tonto' ' shale just above massive sandstones near the mouth of Bass Canyon, on the 

 south side of the Grand Canyon of the Colorado, southeast of Powells Plateau; Ijoth in the Grand Canyon of the Colo- 

 rado, Arizona. 



A siagle ventral valve of this species, or a closely related form, occurs in the following 

 locality : 



Middle Cambrian: (9o) Siliceous limestone about 15 feet (4.6 m.) above the Coronado quartzite [Lindgren, 1905, 

 p. 3], 0.5 mile (0.8 km.) southwest of Milk ranch, on the first spur north of the one which the main road follows, Clifton, 

 quadrangle (U. S. Geol. Survey), Graham County, Arizona. 



