478 CAMBRIAN BRACHIOPODA. 



has been broken away toward the apex. His second figure [1852, PL I b, fig. 12] is a partially 

 covered dorsal valve which shows the characteristic form and the concentric striae of the species. 

 His description [1852, p. 583] is as follows: 



This species has a greater circumference and superficial area than any of the others hitherto discovered in F. 1. 

 Shell nearly oval, rather fiat; beak blunt, and not projecting beyond the general contour of the shell, and formed 

 more after the manner of the beaks of Terabratulaa. A few faint concentric stria;. Length 11/16 of an inch; width 

 8/16 of an inch. 



This species occurs in the Lingula and Obolus grits, member c, near Mountain Island, at the Dalles of the St. Croix, 

 and elsewhere in Wisconsin. 



James Hall did not have the type before him when he described the species. He identified 

 a form from the lower bed at Trempealeau, which he regarded [1863, p. 125] as the typical 

 form of the species. The original type came from Mountain Island, in the Mississippi just 

 above the mouth of Trempealeau River. It also occurs at about the same horizon 10 miles 

 lower down on the west shore of the river, opposite the mouth of Black River. In general 

 form, this species somewhat resembles Lingulella hillingsiana (Wliiteaves) from Newfoundland, 

 but it differs from that species in the character of the surface marldngs and that of the interior 

 markings and scars, especially those of the dorsal valve. The position of the main vascular 

 sinus of the dorsal valve distinguishes it from other species of which we haA^e the interior mark- 

 ings. In a specimen of the ventral valve (PI. XXVIII, fig. If) there appears to be a unique 

 marldng (y) in the central anterior portion of the valve. It recalls the heart-shaped pit (x) 

 of Oholus and Lingulella acutangula (Roemer) (PI. XVII, fig. If), but it is so far away from 

 the normal position of that pit that it appears to be the result of a malformation or an impression 

 in the cast which accidentally resembles the outline of the heart-shaped pit. 



Formation and locality. — Upper Cambrian: "St. Croix sandstone" at the following localities: (80) 0.66 mile 

 (1.1 km.) southwest of the railway depot at Menomonie, Dunn County; (100) near Menomonie, Dunn County; and 

 (98) near Eau Claire, Eau Claire County; all in Wisconsin. 



Middle Cambrian: (84 and 84f) "St. Croix sandstone," at Dresbach opposite the mouth of Black River, Winona. 

 County; (84s) near Dakota, Winona County; and {33Se) on Mountain Island, Minnesota, in Mississippi River just above 

 the mouth of Trempealeau River; all in Mimiesota. 



(328g) Wisconsin shore of the Mississippi, near Trempealeau, Trempealeau County; and (328e) "St. Croix sand- 

 stone" at St. Croix Falls, Polk County; both in Wisconsin. 



A closely related if not identical species occurs at the following locality. A ventral valve 

 from this locality is illustrated in Plate XXVIII, figure Ij. 



Middle Cambrian: (88a) Limestone about 100 feet (30.5 m.) above the quartzitic sandstone at the base of the- 

 Cambrian in the northern suburbs of Deadwood, Black Hills, South Dakota. 



LiNGXILELLA ARGUTA (Walcott). 



1/ 



Plate XXIV, figures 5, 5a-b. 



Lingula? manticulaWBiTB (in part), 1874, LT. S. Geog. Surveys W. 100th Mer., Prelim. Rept. on Invertebrate Fossils^ 

 pp. 9-10. (Described as a new species, including specimens referred to both Lingulella arguta and L. manticula.)' 



Lingula ? mantiada White (in part), 1877, U. S. Geog. Surveys W. 100th Mer., vol. 4, pp. 52-53, PL III, fig. 2a (not 

 fig. 2b). (Described and discussed. The specimen represented by fig. 2a is redrawn in this monograph, Pl- 

 XXIV, fig. 5. The specimen represented by fig. 2b is referred in this monograph to Lingulella manticula.) 



Oholus {Lingulella) argutus Walcott, 1898, Proc. U. S. Nat. Mus., vol. 21, p. 396. (Described and discussed as below 

 as a new species.) 



General form ovate, with the ventral valve obtusely acuminate; valves moderately con- 

 vex. Exterior surface of the shell unknown. Very fine radiating strise and concentric Imes 

 of growth occur on the outer surface of the inner layer of the shell. The shell appears to be 

 of medium thiclcness and formed of a thm outer layer and one or more thin inner layers or- 

 lamellae. The type specimen of the ventral valve has a length of 6 mm. and a width of 4.5 mm. 



Observations. — This species is founded upon one of the specimens illustrated by White- 

 [1875, PI. Ill, fig. 2a] as Lingula f manticula. The broadly ovate form of the ventral valve 

 clearly distinguishes it from that species. From the associated fragments of trilobites it evi- 

 dently occurs at a lo"wer horizon m the Middle Cambrian. A dorsal valve from the same localitj^ 



