OBOLIDiE. 461 



The specific name is derived from "Escasonie," a local name for that part of Cape Breton 

 in which the species occurs. 



Formation AND locality. — ^tTpper Cambrian: (325 [Matthew, 1903, p. SOS]) Arenaceous shales possibly from the 

 horizon of the Peltura fauna {Division C3b), on McAdam shore; and (lOr)" arenaceous shales of Division C3a? of Mat- 

 thew at McAdam shore; both on East Bay, east of Bras d'Or Lake, southeastern Cape Breton, Nova Scotia. 



Middle? Cambrian: flOo'l<» Arenaceous shales in the railroad cut on the shore of Brasd'Or Lake, atBarachois; and 

 (llz) sandstone on Big Ridge, 2 miles (3.2 km.) south of Marion Bridge, on the canal of John McDougald; both in 

 southeastern Cape Breton, Nova Scotia. 



Obolus (Westonia) euglyphus (Walcott). 



Plate XLVIII, figures 1, la-f. 



Obolus (Lingulella) euglyphus Walcott, 1898, Proc. U. S. Nat. Mus., vol. 21, pp. 402-403. (Described and dis- 

 cussed essentially as below as a new species.) 

 Obolus (Westonia) euglyphus Walcott, 1901, Proc. U. S. Nat. Mus., vol. 23, p. 691. (Merely changes generic reference.) 



General form ovate, with the ventral valve subacuminate, and the dorsal valve broad 

 ovate in outline. There is some range of variation in the outline of the valves; this may be 

 seen by comparing figures 1, lb, and Ic of Plate XLVIII. The convexity of the valves is 

 fairly strong and is nearly the same in each. A ventral valve 11 mm. in length has a width of 

 8 mm., convexity 1.5 mm.; and a dorsal valve 9 mm. in length has a width of 8 mm., con- 

 vexity 1.5 nun. 



The outer surface of the shell is marked by strong concentric lines and strise of growth 

 and a complex system of lamellose striae of the type of those on Oholus ( Westonia) ella (Hall 

 and Whitfield). The strife have a transverse direction, are irregular, and sometimes inosculate. 

 They are somewhat coarser than those on the surface of 0. ( TF.) ella (PL XLVII, fig. 1 1) 

 and finer than those of 0. ( TF.) aurora (Hall) (PI. XLVI, figs. Ih and Ig). They are also less 

 irregular than those of 0. ( IF.) ella, and more so than those of 0. ( W.) aurora, the result being 

 a surface character intermediate between those of the species mentioned. When the outer layer 

 is exfoliated the surface of the inner layer is marked by numerous fine, radiating strise (PI. 

 XLVIII, fig. lb) and concentric lines of growth. The cast of the inner gurface of the shell 

 shows rather numerous papilla that fiU the pits or punctse in the shell. The shell is strong 

 and formed of a thin outer layer and several inner layers or lamellse that are arranged very 

 much as in Lingulella acutangula (Roemer) (PI. XVII) . 



As shown by casts of the interior the cardinal area of the ventral valve is rather long and 

 well extended out on the cardinal slopes. It is divided at the center by a cast of a strong, 

 rather deep pedicle furrow, and about three-fifths of the distance between the pedicle furrow 

 and the lateral margin by a sharp, narrow flexure line. The stride of growth cross the area 

 parallel to its base. Only a few traces of them are preserved in the pedicle furrow. The area 

 formed a thin shelf between the pedicle groove and the lateral margins, the undercut extending 

 far back under the area as in L. acutangula. This is shown in the cast by a tliin projection 

 of the embeddmg rock over the area (PL XLVIII, figs. Ic and Id). The area of the dorsal 

 valve is lower and less pronunent. It arches forward at the median fine and extends well 

 out on the cardinal slopes. 



The cast of the visceral cavity (v) of the ventral valve includes the heart-shaped pit (x) 

 and a slight trace of the trapezoidal area, in which the central muscle scars and the middle and 

 outside lateral muscle scars occur. There are no traces of a median septum ia the ventral 

 valve, and it is only sHghtly indicated in one specimen of the dorsal valve. This is owing, 

 however, more to the condition of preservation of the specimen than to the character of the 

 septum. No muscle scars are clearly defined in either valve. Of the vascular sj^stem the 

 main or trunk sinuses are fairly well shown in the ventral valve (PL XLVIII, figs. Ic and Id), 

 but less so for the dorsal valve (PL XLVIII, fig. le). 



Observations. — This form has the general shape of Lingulella acutangula (Roemer), but 

 differs in being more ovate; it also differs in the arrangement of the markmgs on the interior 



a The specimens from Localities lOo and lOr are somewhat doubtfully referred to this species. 



