BILLINGSELLID^. 759 



BiLLINGSELLA ORIENTALIS (Whitfield). 



Plate LXXXVI, figures 2, 2a-b. 



Orthisina orientalis Whitfield, 1884, Bull. Am. Mus. Nat. Hist., vol. 1, p. 144, PI. XIV, fig. 6. (Described and 

 discussed as a new species. Fig. 6 is copied in this monograph, PL LXXXVI, fig. 2.) 



Orthisina orientalis Whitfield, Walcott, 1886, Bull. U. S. Geol. Survey No. 30, p. 120, PI. VII, fig. 6. (Original 

 description, Whitfield, 1884, p. 144, copied and species discussed. Fig. 6 is copied from fig. 6 of the preceding 

 reference.) 



Orthisina orientalis Whitfield, Walcott, 1891, Tenth Ann. Rept. U. S. Geol. Survey, p. 613, PI. LXXII, fig. 8. (Men- 

 tioned. Fig. 8 is copied from Whitfield, 1884, PL XIV, fig. 6.) 



Billingsella orientalis (Whitfield), Hall and Clakke, 1892, Nat. Hist. New York, Paleontology, vol. 8, pt. 1, p. 230. 

 (Merely changes generic reference.) 



Billingsella orientalis (Whitfield), Walcott, 1905, Proc. U. S. Nat. Mus., vol. 28, pp. 239-240. (Described and dis- 

 cussed as below.) 



The original description by Whitfield follows : 



Shell quadrangular in outline, somewhat higher than wide, with vertical and subparallel lateral margins, and 

 broadly rounded base. Cardinal line rapidly sloping from the apex to the extremities, which are slightly rounded. 

 Hinge line straight, as long as the greatest width of the shell. Cardinal area broad and high, divided in the middle 

 by a triangular foramen, which is about as high as wide. Surface of the ventral valve moderately convex, marked 

 by very fine radiating striae and also by several concentric lines of growth. Filling of the rostral cavity and foramen 

 large and prominent. Specimen, a cast in shale, of the ventral valve only. 



Observations. — The type specimen as described above is flattened in the shale, and also 

 appears to be compressed laterally. Uncompressed specunens referred to this species, from 

 the siliceous limestones east of Swanton show the ventral valve to have been rather strongly 

 convex, and the dorsal valve moderately so. The outer surface as shown in the cast indicates 

 that it was somewhat like that of Billingsella color ado ensis, but that it differs in having finer 

 and more numerous threadlike costsB. A few traces of concentric strise and lines of growth 

 are preserved. The material is very unsatisfactory, but it is sufficient to indicate that the 

 genus occurs in association with Olenellus thompsoni in the upper beds of the Lower Cam-brian 

 section. 



FoKMATioN AND LOCALITY. — Lowcr Cambrian: (25a) Limest.one on the Hall (Donaldson's) farm, 2 miles (3.2 km.) 

 east of Swanton; (26) sandstone northeast of the Gorman farm buildings, east of Highgate Springs; (319m) shales of 

 No. 6 of the section at Parker's quan-y [Walcott, 1891b, p. 278], near Georgia; and (319g [Whitfield, J8S4, p- 144]) shales 

 at Parker's quarry, near Georgia; all in Franklin County, Vermont. 



Billingsella plicatella Walcott. 



Text figure 1, page 299; Plate LXXXVI, figures 3, 3a-n. 



Billingsella plicatella Walcott, 1905, Proc. U. S. Nat. Mus., vol. 28, pp. 240-241. (Described and discussed as below 

 as a new species.) 



Shell irregularly subquadrate in outline. In the ventral valve the cardinal line slopes 

 toward the beak at an angle of from 5° to 10°, whereas in the dorsal valve it is usually about 

 1° to 3°. The greatest width of the shell is about the middle. There is some variation in 

 the relative proportions of length and breadth. Usualty, however, the ventral valve is fully 

 as long as wide, while in the dorsal valve it is slightly transverse. The ventral valve is rather 

 strongly convex, the dorsal valve being less so. A low, broad mesial sinus occurs on nearly 

 all specimens of the dorsal valve, and sometimes a distinct sinus on the ventral valve. 



The surface is marked by costae that give it a plicated appearance in many specimens; 

 also, concentric lines of growth and very fine, slightly undulating strise. On some shells the 

 costse and surface markings have been almost entirely removed by abrasion while in others 

 they are clear and distinct. There is a considerable range of variation in the strength and form 

 of the surface markings. These are illustrated by the figures on Plate LXXXVI. 



When the shell is exfoliated, fine radiating lines occur toward the front margins. The 

 average size of the shell gives a width of about 8 mm., and in the ventral valve a nearly equal 

 length. One specimen has a width of 11 mm. 



