520 CAMBEIAN BRACHIOPODA. 



LiNGULELLA MOSIA (Hall). 



Plate XVIII, figures 1, la-f. 



Lingula mosia Hall, 1863, Sixteenth Ann. Kept. New York State Cab. Nat. Hist., p. 126, fl. VI, figs. l-3a. (Described 



and discussed as a new species ; see below. ) 

 Lingula mosia Hall, 1867, Trans. Albany Inst., vol. 5. pp. 102-103, PI. I, figs. l-3a. (Copy of preceding reference.) 

 Lingula mosia Hall, Sardeson, 1896, Bull. Minnesota Acad. Nat. Sci., vol. 4, No. 1, pt. 1, p. 95. (Discussed from a 



new locality.) 



The original description by Hall follows: 



Shell small, subelliptical, or ovate-spatulate, little convex, concentrically striated. The slopes below the beak 

 are sometimes nearly straight for a short distance, and often curving from the beak to the base. The specimens are for 

 the most part impressions in sandstone, with little of the shell remaining, but the form is very distinct from any of 

 the described species; and being limited in vertical range, and with a somewhat wide horizontal extension, it becomes 

 of interest in its associations. 



The study of a large number of specimens has added little to the knowledge of tliis species. 

 Nearly all the shell structure has been removed, and only more or less imperfect casts remain 

 in the sandstone. The outer surface is marked by fine concentric strise and lines of growth, 

 and in one cast there is an indication of irregular, almost inosculating stride, such as occur on 

 portions of the surface of Oholus (Westonia) ella (Hall and Whitfield). The few fragments of 

 the shell in the material studied indicate that it was of medium thickness and formed of two 

 or more layers, and that the inner lamellte were marked by fine radiating strise. 



The average size of the ventral valve is about 8.5 mm. in length by 7 mm. in width. The 

 dorsal valve is a little shorter in proportion to the width. 



The area of the ventral valve is high; it is broken midway by a strong narrow pedicle 

 groove, and on each side, well out toward the margin, by very narrow flexure lines. Strong 

 striae of growth cross the area parallel to its base. They arch transversely over the cast of 

 the pedicle furrow. The area of the dorsal valve is well defined; it is crossed by fine strise 

 of growth, and marked by oblique flexure hnes that outline a rather broad space between 

 them. 



The casts of the interior of the ventral valve show traces of the visceral cavity and main 

 vascular sinuses, and the central and anterior lateral muscle scars have been seen in the dorsal 

 valve. 



Ohservations. — The broad, almost subquadrate outhne of some of the specimens of the 

 dorsal valve suggest Oholus ( ^Vestonia) ella (Hall and Wliitfield) (PL XL VII) and there is a 

 trace of the surface of the latter. A closer comparison of the two shows that 0. ( W.) ella is a 

 broader shell, Avith a characteristic surface ornamentation. Lingulella mosia may be the Upper 

 Cambrian representative of the Middle Cambrian Oholus ( Westonia) ella. 



Formation and locality. — Lower Ordovician: (364a [Sardeson, 1896, p. 95]) reported by Sardeson from the 

 Oneota dolomite along St. Croix Elver in both Wisconsin and Minnesota. 



Upper Cambrian: (113) "St. Croix sandstone" at La Grange Mountain (or Barn Bluff), near Eed Wing, Goodhue 

 County, Minnesota. 



(78 and 78s) " "St. Croix sandstone," quarry near St. Croix River in suburbs of Osceola, Polk County; (86) & 

 "St. Croix sandstone" near Prairie du Sac, Sauk County; (85x and S85x) upper beds of the "St. Croix sandstone" near 

 Mazomanie, Dane County; (99a) "St. Croix sandstone" near Pilot Knob, Adams County; (100) "St. Croix sand- 

 stone" near Menomonie, Dunn County; (79 and-79s) "St. Croix sandstone" near Hudson, St. Croix County; (98x) 

 "St. Croix sandstone" near Eau Clah-e, Eau Claire County; (78b) "St. Croix sandstone" 50 feet (15.2 m.) above 

 St. Croix River, near the landing at Osceola, Polk County; (98a) "St. Croix sandstone" at Marine Mills, Wash- 

 ington County; (86) "St. Croix sandstone," at Van Ness's quarry, Gibraltar Bluff, Lodi, Columbia County; and 

 (85s) "St. Croix sandstone" at Prairie du Sac, Sauk County; all in Wisconsin. 



(364) St. Lawrence formation of Sardeson [1896, p. 95], in both Wisconsin and Minnesota. 



(341a) Sandstone at McGregor, Clayton County, Iowa. 



oThe species also occurs in Locality 78c (p. 214). 



6 86 is the type locality, though the specimens in the United States National Museum collections to which that number is assigned were 

 collected later than the type specimens. 



