OBOLIDiE. 523 



A single specimen of a ventral valve 4 mm. in length that is much like the corresponding 

 valve of Lingulella ora occurs at the following locality. More and better material is needed 

 before an identification can be made that is more than tentative. 



Middle Cambrian: (11m) Drill cores of limestone in the Bonneterre limestone at horizons 10 and 20 feet (3 and 

 6 m.) above the Lamotte sandstone at Flat River, St. Francois County, Missouri. 



Lingulella oweni (Walcott). 

 Plate XVIII, figures 5, 5a-f. 



Oholus {Lingulella) oweni Walcott, 1898, Proc. U. S. Nat. Mus., vol. 21, p. 410. (Described and discussed essentially 

 as below as a new species.) 



General form ovate, with the ventral valve obtusely acuminate, and the dorsal valve 

 more broadly rounded posteriorly; valves appear to have been moderately convex, as far as 

 can be determined from the flattened specimen in the shaly sandstones. Surface of shell 

 marked by concentric lines and striae of growth and indistinct, radiating strise. There are 

 no traces of the interior markings observed. The shell is of medium thickness; none of the 

 specimens show how it was built up, farther than that there were obhque lamellse attached to 

 the outer layer in the anterior portion of the valve. The largest ventral valve from Gibraltar 

 Blufi' has a length of 16.5 mm.; width, about 12 mm.; an associated dorsal valve 14 mm. in 

 length, has a width of 11 mm. as it occurs flattened on the surface of the sandstone. A 

 smaller shell referred to this species from Osceola averages from 6 to 8 mm. in length. 



As shown in the cast of an interior of a shell, the area is rather long, and divided midway 

 by a sharp pedicle furrow; the flexure lines are situated about midway between the cast of 

 the pedicle furrow and the lateral margin. The area formed a thin shelf between the pedicle 

 groove and the lateral margins, the undercut extending far back under the area; a broken 

 portion of this is preserved on the cast illustrated by figure 5a. 



One cast of the interior of a ventral valve shows a slight trace of the visceral area (PL 

 XVIII, fig. 5d). In a cast of a dorsal valve (fig. 5b) both the central and anterior lateral 

 muscle scars are somewhat indistinctly preserved. 



Observations. — This species is most nearly related to Lingulella ampla (Owen). It difl'ers, 

 as far as can be determined from the material for comparison, in being less elongate and in 

 the position of the central and anterior lateral muscle scars in the dorsal valve, as may be 

 seen by comparing Plate XVIII, figure 5b, with Plate XXVIII, figure Ig. The typical form 

 of this species is represented on Plate XVIII, figures 5, 5b, and 5c, and a smaller form, which 

 has been referred to it, by figures 5d, 5e, and 5f. 



The species differs strongly from Obolus (Westonia) stoneanus (Whitfield) in its surface 

 markings, although the outline of the valves is almost the same in the two species. 



The specific name was given in honor of Dr. D. D. Owen. 



Formation and locality. — ^Tipper Cambrian: (78c) "St. Croix sandstone" at Osceola, Polk County; (86) "St. 

 Croix sandstone" at Van Ness's quarry, Gibraltar Bluff, Lodi, Columbia County; (85z) "St. Croix sandstone" at 

 Madison, Dane County; (85a) "St. Croix sandstone" at Brown's quarry, Prairie du Sac, Sauk County; and (85s) 

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



(97) "St. Croix sandstone" at Reads Landing, foot of Lake Pepin, Wabasha County, Minnesota. 



Lingulella perattenuata (Whitfield). 

 Plate XXI, figures 1, la-i. 



I/ingulepis perattenuatus Whitfield, 1877, U. S. Geog. and Geol. Survey Rocky Mtn. Region, Rept. Geol. Black Hills 

 of Dakota, Prelim. Rept., p. 9. (Described and discussed as on p. 524 as a new species.) 



I/ingulepis perattenuatus Whitfield, 1880, U. S. Geog. and Geol. Survey Rocky Mtn. Region, Rept. Geol. and Re- 

 sources Black Hills of Dakota, by Newton and Jenney, p. 337, PI. II, figs. 7-9. (Copy of preceding refer- 

 ence. The specimens represented by figures 7, 8, and 9 are redrawn in this monograph, PI. XXI, figs, li, Ih, 

 and lb, respectively.) 



