590 CAMBRIAN BRACHIOPODA. 



The area of the ventral valve is low and rises from the edge of the valve to meet the beak at 

 an angle of 30° to 45°; it extends well out on the cardinal slopes before merging into them; a 

 narrow furrow divides it midway. 



The anterior margin of the area adjoining the false pedicle furrow forms a tooth or knob- 

 like projection (PI. LV, fig. le) that forms a deep recess next to the cast of the pedicle tube in 

 the casts of the interior of the ventral valve (fig. If). The surface of the area is marked by fine 

 transverse striae. On each side of the pedicle tube there is a strong undercut which in the cast 

 is replaced by a toothlike projection. The area of the dorsal valve extends nearly as far out 

 on the cardinal slopes as that of the ventral; it is marked midway in the cast by two ridges 

 that converge toward the median line at the posterior margin; these ridges represent furrows 

 such as occur on the areas of some species of Oholus and Lingulella at the side of the flexure 

 lines {Lingulella acutangula (Roemer), PI. XVII, fig. Ih). They are also present in the dorsal 

 valve of Oiolella diromatica Billings. 



The pedicle tube or foramen is beautifully shown in numerous casts of the ventral valve. 

 When the shells are compressed the cast of the tube rests so nearly on the area that one is led 

 to doubt the existence of shell between the area and the tube. (See PI. LV, figs. If, Ig, 3c.) 

 In uncompressed specimens the cast of the tube extends upward and backward as shown 

 by figure Ih. The cast shows a minute apex and trumpet-shaped base. None of the speci- 

 mens show the exterior forarninal opening, nor has it been seen in any species of the genus. 



The strong pedicle furrow shoMTi on the cardinal area in Plate 



LV, figure le, does not exist on the specimen, except as indicated 



by two faint lines. The true pedicle tube opening is shown beneath 



/ _ _ _ the area, as represented in figure, 51. This was drawn from the 



same specimen as that represented in Plate LV, figure le. 



Figure 51.— 06o!eiia o((a7?(ico Walcott. , , j_ ii i • j.i j. • ^ •^ 



View of ventral valve, tipped back The musclc scars are not Well preserved m the material avail- 



to show pedicle opening beneath g^^jg fpp study. The position of the transmediau scars (i) is indi- 



thearea(X4). (The same specimen i • xi x i i j.i • j 



is shown in a diflerent position in PI. catcd On cach vaive; also in the ventral valve the space occupied 

 Lv.flg. le.) The specimen is from |j„ ^^g central, middle lateral, and outside lateral muscle scars. 



Locality So, LowerCambrian shales ^„ ,, i i • ,i • • i xi x i 



at Smith Sound, Trinity Bay, New- Of the vascular marliings the main sinuses or the ventral 



loundiand (u. s. Nat. Mus. Cat. ^alve are fairly well shown, also the outlines of the parietal scar 

 (PI. LV, fig. Ig). The presence of a short median ridge is indicated 

 on a cast of the dorsal valve (fig. li). 



Observations. — This small but very interesting species is most nearly related to 0. cJiro- 

 matica Billings. It is nearly the same size, has the same type of shell structure, and probably 

 the same surface characters. It differs in being less convex, in having a more transverse dorsal 

 valve, less elongate ventral valve, and the narrower marginal border on the inside of the shell, 

 as shown by comparing Plate LV, figure Ih, with Plate LIV, figure Ih. 



The separated valves occur in immense numbers in the shales above the limestone on 

 Smith Point and they are also abundant in a ferruginous limestone at Manuels. The mode 

 of occurrence of the species is very much like that of 0. cJiromatica, of which it appears to be 

 the Atlantic coast province representative; hence the specific name. 



Formation and locality. — Lower Cambrian: (5o) Just below the Middle Cambrian in shales on Smith Point; 

 and (5n) shales about 275 feet (84 m.) below the horizon of Locality 5o on Smith Point; both in Smith Sound, 

 Trinity Bay, Newfoundland. 



(5t) Shale and limestone nodules about 20 feet (6 m.) above the base of the Cambrian, on Eedrock Point near 

 Chappie Cove, Hollywood Point; (41) sandstone [see Walcott, 18911), p. 260, for position in section] on Manuels Brooh; 

 (41a) limestone [Walcott, 1891b, p. 260] on the mainland beneath Topsail Head; and (5p) limestone 300 feet (91.4 m.) 

 southeast of the railway station, Manuels; all on Conception Bay, Newfoundland. 



(9n and 336e) Dark-purplish siliceous shales on Pearl Street, North Weymouth, Norfolk County; (326f [Burr, 

 1900, p. 47]) 0.5 mile (0.8 km.) south of North Weymouth, Norfolk County; and (326d) station 2 of Grabau [1900, 

 p. 610], near North Attleboro, Bristol County; all in Massachusetts. 



Specimens compared with this species occur at the following locality: 



Lower Cambrian: (59m) Weisner quartzite in the Roan iron mine, Bartow County, Georgia. 



