OBOLID^. 481 



in the fine sandstone, marked by lines of growth, and fine, slightly undulating striae ; the inner 

 surface is marked by somewhat irregularly scattered pits or punctse, some of which are unusually 

 large for the size of the shell. The few remaining traces of the shell indicate that it was relatively 

 thin. The largest well-preserved cast of the ventral valve has a length of 5 mm., with a width 

 of 4.5 mm. The dorsal valves are a little shorter, the length and breadth being nearly the 

 same. Casts of the interior of the ventral valve show the presence of a rather long area divided 

 midway by a narrow, clearly defined cast of a pedicle groove; traces of flexure lines are also 

 preserved. The area of the dorsal valve is proportionately shorter than that of the ventral 

 valve; traces of the visceral cavity (v) and the base of the main vascular sinuses (vs) are pre- 

 served in a few specimens and in one specimen the anterior lateral muscle scars appear to be 

 present. 



Observations. — In the form of the valves this species is somewhat similar to Lingulella 

 grandis (Matthew) (PI. XXXVIII); otherwise it appears to be quite distinct from any other 

 described species. It has a long cardinal area and a narrow, deep pedicle furrow on the ventral 

 valve. 



Formation and locality. — Middle Cambrian : (10a) Sandstones of the Rome formation, in west railroad cut 

 through Shooks Gap; and (10b) limestones of the Rome formation at the western end of the central railroad cut through 

 Shocks Gap; both in Bays Mountains, 10 miles (16.1 km.) southeast of Knoxville [Keith, 1895, areal geology sheet], 

 Knox County, Tennessee. 



I Lingulella sella (Walcott). 



Plate XIX, figures 2, 2a-q; Plate XXXVI, figure 4. 



Obolm (Lingulella) helium Walcott, 1898, Proc. U. S. Nat. Mus., vol. 21, pp. 397-398. (Described and discussed as a 

 new species.) 



Oholus {Lingulella) bellus Walcott (in part), 1901, Proc. U. S. Nat. Mus., vol. 23, pp. 685-687. (Described and dis- 

 cussed, including specimens now referred to Lingulella condnna Matthew and L. lens (Matthew).) 



Oiolus (Lingulella) bellus Walcott, Matthew, 1903, Geol. Survey Canada, Kept. Cambrian Rocks Cape Breton, p. 204. 

 (Says "0. (L.) bellus" does not include "Lingulella concinna" .) 



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

 to ovate quadrate; valves moderately convex as far as can be determined from the somewhat 

 compressed specimens as they occur in the sandy shales. The small ventral valves are more 

 acuminate than the large ones and the smaller dorsal valves are more elongate. The change 

 in form is slight from one to another specimen in the series, but the two extremes are so difl'erent 

 that without the connecting series two species could be determined. 



Surface of shell with numerous concentric lines of growth and fine radiating lines. The 

 inner layers are marked by concentric lines and numerous fine radiating striae. 



The shell is relatively thin over the anterior portions and stronger near the cardinal mar- 

 gins. It is formed of a very thin outer layer, with one or more thin layers or lamellae. The 

 casts of the interior surface of the ventral valve show numerous papillae arranged in concentric 

 lines on the posterior half of the shell. These correspond to the punctae of the inner surface. 



A large ventral valve has a length of 22 mm.; width, 15 mm.; and a dorsal valve 18 mm. 

 in length had a width of 14 mm. The specimens in the collection average from 2 to 3 mm. 

 smaller than those measured. 



The cast of the area of the ventral valve shows that it was rather long and extended well 

 out onto the cardinal slope; it is divided midway by a strong pedicle furrow, and toAvard the 

 lateral margin by a narrow flexure line. The area is marked by fine striae of growth parallel 

 to the margin. The area of the dorsal valve is rather short, but it extends laterally well out 

 on the cardinal slopes. The shallow curve corresponding to the pedicle groove of the larger 

 valve is wide and clearly defined. 



The casts of the interior of the valves show almost no traces of the vascular markings or 

 muscle scars. Only the central and anterior lateral muscle scars and the main vascular sinuses 

 have been observed in the ventral valve. 

 62667°— vol 51, pt 1—12 31 



