OBOLID^. 395 



margin of the dorsal valve, and in the position of the central muscle scars. Specimens from the 

 limestone just above the shales at Mine Lamotte are moderately convex and more elongate 

 than those compressed in the shale. Some shells suggest the outline of Lingulella acutangula 

 (PL XVII). 



Formation and locality. — Upper Camlbrian: (7d) Shales in second cliff 0.125 mile (0.2 km.) west of Peak, 

 3 miles (4.8 km.) south of Clinton, Briceville quadrangle (U. S. Geol. Survey), Anderson County; and (122a) shale 

 at the headwaters of Forgey Creek, northwestern part of the Greeneville quadrangle (U. S. Geol. Survey), Hawkins 

 County; both in Tennessee. 



Middle Cambrian: {ll])a Shale and limestone in the basal part of the Bonneteire limestone, Mine Lamotte, Madison 

 County; (369f) limestone at Fredericktown, Madison County; (11m) drill cores of limestone at horizons 10 and 20 

 feet (3 and 6 m.) above the Lamotte sandstone, 'St. Francois County; and (369h) shale at Mine Lamotte, Madison 

 County; all in Missouri. 



(331) Rogersville shale 1 mile (1.6 km.) south of Fletcher, Greene County, Virginia. 



(102) Rogersville shale just south of road, one-half mile (0.8 km.) southwest of Rogersville on the road to Melinda 

 Ferry [Keith, 1896a, areal geology sheet]; (103) second shale south of the ridge of sandstone in the Rome formation 

 ("Town Knobs"), on the road from Rogersville to Dodson Ford, near the line between the Morristown and Greene- 

 ville quadrangles (U. S. Geol. Survey); (121) Rogersville shale, road just east of Harlan Knob, 4 miles (6.4 km.) 

 northeast of Rogersville [Keith, 1905, areal geology sheet]; (101b) Rogersville shale, just east of the schoolhouse, 3.5 

 miles (5.6 km.) southwest of Rogersville on the road to Melinda Ferry [Keith, 1896a, areal geology sheet]; and (124a) 

 shales (Nolichucky?) overlying the limestone which rests on the Rogersville shale, on Big Creek, southeast of Harlan 

 Knob, 4 miles (6.4 km.) northeast of Rogersville [Keith, 1905, p. 4, and areal geology sheet]; all in Hawkins County, 

 Tennessee. 



(140a) Shales 200 yards (182.9 m.) east of Thomas Mills, 5 miles (8 km.) north of Cave Spring [Hayes, 1902, his- 

 torical geology sheet], Floyd County, Georgia. 



Obolus lamborni minimus (Walcott). 

 Plate XXV, figures 4, 4a-b. 



Obolus {Lingulella) lamborni minimus Walcott, 1898, Proc. U. S. Nat. Mus., vol. 21, p. 407. (Discussed as below as 

 a new variety.) 



This variety in its ventral valve closely resembles tlie adult form of the ventral valve of 

 Obolus lamborni (Meek). The dorsal valve also has the same general form as most of the dorsal 

 valves of the species. In comparing, however, the young specimens of the same size with the 

 variety minimus the ventral valves appear to be more obtuse in the young of 0. lamborni. 



Formation and locality. — Middle Cambrian : (101 and 101a) b Rogersville shale, just above the road in the hill 

 west of the schoolhouse, 3.5 miles {5.6 km.) southwest of Rogersville on the road to Melinda Ferry [Keith, 1896a, areal 

 geology sheet\ Hawkins County; (103a) upper part of the second shale south of the ridge of sandstone in the Rome 

 formation ("Town Knobs"), on the road from Rogersville to Dodson Ford, near the line between the Morristown and 

 Greeneville quadrangles (U. S. Geol. Survey), Hawkins County; (124) shales (Nolichucky?) overlying limestone 

 which rests on Rogersville shale, on Big Creek, southeast of Harlan Knob, 4 miles (6.4 km.) northeast of Rogersville 

 [Keith, 1905, p. 4, and areal geology sheet], Hawkins County; and (118) shales on the Tazewell road, 2 miles (3.2 km.) 

 north of Knoxville, Knox County; all in Tennessee. 



Obolus loperi Walcott. 



^ Plate IX, figures 4, 4a. 



Obolus loperi Walcott, 1898, Proc. U. S. Nat. Mus., vol. 21, pp. 389-390. (Described and discussed as below as a 

 new species.) 



General form subsemicircular, with the ventral valve subacuminate and the dorsal valve 

 broad ovate to circular in outline. Some of the shells are more elongate than in what is consid- 

 ered to be the typical form. This type of variation is also observed in 0. matinalis (Hall) 

 (PL VIII) and other species of the genus. Valves moderately convex as they occur in the 

 sandstone. Surface of the shell marked by concentric lines and fine striae of growth and very 

 narrow radiating undulations that are more or less interrupted by the concentric lines of growth. 



o Locality llj is given as the type locality, though the type specimens were collected from the Mine Lamotte locality long before the 

 collection to which this number was assigned. The two localities are believed to be the same. 

 *» 101a is the type locality. 



