OBOLID^. 507 



v302s) Dark siliceo- s shale in a quarry in Last Chance Gulch, south slope of Mount Helena, 1.5 miles (2.4 km.) south 

 of Helena; and (4u) shales in the Gallatin formation of Peale [1893, PI. IV], northwest side of canyon, 0.5 mile 

 (0.8 km.) south of Helena; both in Lewis and Clark County, Montana. 



/ LiNGULELLA ? HUMiLLiMA (Barpande 



Plate XXX, figure 12. 



Idngula humillima Barrande, 1868, Faune silurienne des environs de Hof, en Bavifere, p. 101, fig. 70. (Character- 

 ized in French as a new species. Fig. 70 is reproduced in this monograph, PI. XXX, fig. 12.) 



Idngula humillima Barrande, 1868, Neues Jahrb. fiir Mineralogie for 1868, p. 691, unnumbered plate, fig. 70. 

 (Copy of preceding reference.) 



Tills species was described from a single small, oval, compressed shell. The author states 

 that its appearance does not permit its identification with any other described species. The 

 shell has a length of 5 mm.; width, 3.5 mm. 



Formation and locality. — Passage beds between the Upper Cambrian and the Ordovician: (303c [Barrande, 

 X86Sa, p. 101]) Suburbs of Hof ; and (303f [Pompeckj, 1896a, pp. 7 and 8]) railway cut near Schellenberg, a little dis- 

 tance back of the railway station at Neuhof, near Hof; both in Bavaria, Germany. 



LiNGULELLA INO (Walcott). 



Plate XXVI, figures 4, 4a-b. 



Obolus (Lingulella) ino Walcott, 1898, Proc. U. S. Nat. Mus., vol. 21, pp. 406^07. (Described and discussed essen- 

 tially as below as a new species.) 



Shell a little smaller than the average of the species of the genus. General form ovate, 

 with the ventral valve subacuminate and the dorsal valve ovate in outline. There is some 

 range of variation in the outhne of the valves, but as a whole they do not vary more than the 

 difference shown in the ventral valve by Plate XXVI, figures 4, 4a. The convexity of the 

 valves is fairly strong, as the shells are preserved in the somewhat shaly sandstones. Ventral 

 valves 7 mm. in length have a width of from 5.5 to 6 mm.; a dorsal valve 5 mm. in width has 

 a length of 5.25 mm. 



As far as may be determined from the casts, the outer surface is marked by concentric 

 lines and striae of growth, and the inner surface by radiating striae and concentric fines of 

 growth and scattered pits or punctse. The sheU appears to have been rather thick, and built 

 up of a thin outer layer and numerous lamellae that over the anterior two-thirds of the shell 

 were obfique to the outer layer; the edges of the lameUae show very plainly when the outer 

 layer is removed. 



The area of the ventral valve as shown by casts of the interior is of medium length, divided 

 midway by a narrow elevated cast of the pedicle furrow, and again by a narrow flexure line 

 about halfway between the pedicle groove and the lateral margin; striae of growth cross it 

 paraUel with the base. The area of the dorsal valve is relatively long, with the flexure lines 

 clearly defmed. The interior markings shown in the cast of the ventral valve are the main 

 vascular sinuses and the outfine of the visceral area; in the dorsal valve only traces of the 

 visceral area and main vascular sinuses have been observed. 



Observations. — This species appears to be more nearly related to LingvMla tarpa (Walcott) 

 than to any other of the Middle Cambrian forms. It is a smaUer shell than L. tarpa, and less 

 acuminate. It has the outfine of some of the species of the Atlantic basin fauna such as 

 Lingulella radula Matthew (PL XLV), but it does not appear to be specificaUy identical 

 with any of them. 



Formation and locality. — Middle Cambrian: (13) Sandstones of the Rome formation, 1.5 miles (2.4 km.) east 

 of Post Oak Springs [Hayes, 1894, areal geology sheet], Roane County; (13b) sandstones of the Rome formation, north- 

 east of Rhea Springs [Hayes, 1S94, areal geology sheet], Rhea County; and (11) sandstones and shales of the Rome 

 formation, about 1 mile (1.6 km.) east of Post Oak Springs [Hayes, 1894, areal geology sheet], Roane County; all in 

 Tennessee. 



(13c) Sandstones of the Rome formation, west side of the sandstone ridge about 2.5 miles (4 km.) southwest of 

 Rome [Hayes, 1902, historical geology sheet], Floyd County, Georgia. 



