CAMBRIAN BHACHIOPODA—WALCOTT. 411 



13 imn. in length bas a width of 11 mm.; a dorsal valve 11 mm. long 

 has a width of 10 mm. 



As shown in the cast of the interior of the shell, the area of the ven- 

 tral valve rises gradually from the margin toward the pedicle groove. 

 It is broken midway by the cast of a strong pedicle furrow and a little 

 more than half way up toward the lateral margin by a strong Hexure 

 line; the striae of growth are very fine and cross the area parallel with 

 its base. The cast of tlie undercut shows that the area formed a thin 

 shelf between the ])edicle groove and the lateral margins. The area of 

 the dorsal valve is well defined. As in the ventral valve, the area 

 formed a thin shelf, as shown by the cast of the undercut extending 

 well over the area in several of the specimens. 



The cast of the interior of the ventral valve shows the strongly 

 defined, narrow visceral area, the trapezoidal area in which the central, 

 middle, and outside lateral muscle scars occur; also the anterior lateral 

 muscle scars and unusually stroug main vascular sinuses. In a speci- 

 men not illustrated, what appeared to be lines of growth occur on the 

 ridge in front of the trapezoidal area — a feature that is present in 0. 

 (L.) haycm and 0. matinalis. In a dorsal valve the relatively narrow 

 central vascular area extends forward to nearly the center of the shell; 

 the central and anterior lateral scars are faintly indicated, also trans- 

 median scars and the median se])tum; the main vascular sinuses are 

 unusually deep and well defined. 



OhservaUom. — This species at first inspection might be taken for 

 (t. (/>.) amjdufi. It occurs at the same horizon in association with Dicel- 

 lomuH polita. It differs in being a broader and less elongate shell, in 

 iiaving the visceral area of the dorsal valv.e terminate near the (jenter 

 instead of forward of the center, and, as far as can be determined from 

 the material at hand, in being a thicker shell. It also averages about 

 one-fourth less in size. 



Formation and locality. — Middle Cambrian, St. Croix sandstone, 

 upper beds of the section at Eau Claire, Wisconsin. 



Type.— 1^0. 27331, U.S.N.M. 



OBOLUS (LINGULELLA) POGONIPENSIS, new species. 



Shell rather large, general form ovate, almost ovate-cuneate in the 

 ventral valve; dorsal valve is more ovate. Valves moderately convex. 

 Surface of the shell marked by numerous concentric lines and stria^ of 

 growth and very fine radiating stria;; the finer concentric stria* are 

 slightly irregular, but not nearly so much so as in many species of the 

 subgenus. The outer surface of the inner layer is marked by very fine 

 radiating stria^, also concentric lines of growth. The shell is below 

 the average thickness, and is formed of a thin outer layer and one or 

 more inner layers or lamelhe. 



The largest ventral valve has a length of 15 mm. ; width, 11 mm. As 

 shown by a partial cast, the area is of medium length and divided mid- 

 way by a narrow, strongly marked cast of the jiedicle furrow. 



