OBOLID^. 525 



/ LiNGULELLA PHAON (Walcott). 



Plate XX^a, figures 1, la-e. 



Oholus (Lingulella) phaon Walcott, 1898, Proc. IT. S. Nat. Mus. , vol. 21, pp. 410-411. (Described and discussed 

 essentially as below as a new species.) 



General form ovate, with the ventral valve subacuminate, and the dorsal broadly ovate; 

 valves of moderate convexity. Surface of the shell marked by fine concentric lines and strise 

 of growth, and very fine more or less interrupted radiating striae; when the outer layer is exfo- 

 liated the inner surface is marked by numerous fine radiating striae ; the interior surface as seen 

 in casts is more or less marked by rather large papillae arranged in concentric lines, the papillae 

 corresponding to the pits or puncta? on the inner surface of the shell. The shell is rather thick, 

 and is built up of a thin outer layer and several inner layers or lamellae, the lamelte toward 

 the front being oblique to the outer layer. A large ventral valve 15 mm. in length has a width 

 of 13 mm. ; a dorsal valve 11 mm. long has a width of 10 mm. 



As sho^vn in the cast of the interior of the shell, the area of the ventral valve rises gradu- 

 ally from the margin toward the pedicle groove. It is broken midway by the cast of a strong 

 pedicle furrow and a little more than halfway up toward the lateral margin by a strong flexure 

 line; the striae of growth are very fine and cross the area parallel with its base. The cast of the 

 undercut shows that the area formed a thin shelf between the pedicle 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 broken edges of the undercut between the areas is 

 shown by Plate XXVI, figures lb, Ic, Id. 



The cast of the interior of the ventral valve (PI. XXVI, figs, lb and Ic) shows the strongty 

 defined, narrow, visceral area (v), the trapezoidal area (c) in which the central, middle, and 

 outside lateral muscle scars occur, also the anterior lateral muscle scars (j), and unusually 

 strong main vascular sinuses (vs). In a specimen which is not illustrated, apparent lines of 

 growth occur on the ridge in front of the trapezoidal area (c), a feature that is present in L. 

 hayesi (Walcott) and Oholus matinalis (Hall). In a dorsal valve the relatively narrow central 

 vascular area extends forward nearty to the center of the shell (PI. XXVI, fig. Id); central (h) 

 and anterior lateral (j) scars are faintly indicated, also transmedian (i) scars, and the median 

 septum (s); the main vascular sinuses (vs) are unusually deep and well defined. 



Observations. — This species at first inspection might be taken for Lingulella ampla (Owen) 

 (PL XXVIII). It occurs at the same horizon in association Avith Dicellomus politus (Hall). 

 It differs in having a broader and less elongate shell, with the visceral area of the dorsal 

 valve terminating near the center instead of forward of the center, and, as far as can be deter- 

 mined from the material at hand, in having a tliicker shell. It also averages about one-fourth 

 less in size. 



Formation and locality. — TTpper Cambrian: (98 and 98x)a "St. Croix sandstone" near Eau Claire, Eau Claire 

 Coimtij; and (88a) "St. Croix sandstone" 25 feet (7.6 m.) above the water level near the Knapp, Stout and Company's 

 buildings, Menomonie, Dunn County; both in Wisconsin. 



(84a) "St. Croix sandstone " at River Junction, Houston County, 20 miles (32.2 km.) below Dresbach, Minnesota. 



Lingulella pogonipensis (Walcott). 



Plate XX, figures 3, 3a-c. 



Oholus {Lingulella) pogonipensis Walcott, 1898, Proc. U. S. Nat. Mus., vol. 21, pp. 411^12. (Described and dis- 

 cussed as below as a new species.) 



Shell rather large, general form ovate, almost ovate cuneate in the ventral valve; dorsal 

 valve more ovate. Valves moderately convex. Surface of the shell marked by numerous 

 concentric lines and striae of growth, and very fine radiating striae; the finer concentric striae 

 are slightly irregular, but not nearly so much so as in many species of the genus. The outer 



a. 98x is the type locality. 



