750 



CAMBRIAN BRACHIOPODA. 



Of the species referred to the genus, Billingsella exporreda is one that departs from the 

 typical species in the absence of a strong convex deltidium, and B. dice has a rudimentary 

 spondyUum in the ventral valve, a character not developed in other species of the genus. 



For the relations of Billingsella to Nisusia, see remarks under the latter genus, page 725. 



The genus was named in honor of Mr. E. Billings. 



Billingsella ? appalachia Walcott. 



Plate LXXXVII, figures 2, 2a-b. 



Billingsella ? appalachia Walcott, 1905, Proc. U. S. Nat. Mus., vol. 28, p. 231. (Described as below as a new species.) 



The outline of the dorsal valve is rounded subquadrate. The height and width of the 

 ventral valve are about the same. Dorsal valve slightly transverse. 



The surface is marked by round, very fine, radiating costse, and lines of growth, with very 

 fine interstitial concentric striae. 



The average ventral valve is about 10 mm. in height, with an equal width. The largest 

 shell observed was a ventral valve with a width of 14 mm. 



Cardmal area of the ventral valve rather low. It is divided midway by a rather strong 

 delthyrium. 



Observations. — In form and size this shell is much like that of Wimanella? anomala. It 

 differs in its strongly marked surface characters. All the specimens are flattened in the shale 

 and nothing is known of the interior characters. 



Formation and locality. — Middle Cambrian : (121) Rogersville shale, road jiist east of Harlan Knob, 4 miles 

 (6.4 km.) northeast of Rogersville [Keith, 1905, areal geology sheet], Hawkins County, Tennessee. 



This species is somewhat doubtfully identified from the following locality : 



Middle Cambrian: (14) Limestones overlying the sandstones of the Kome formation, near the wagon road and 

 in a quarry near the railroad track, 7 miles (11.2 km.) southwest of Rome [Hayes, 1902, historical geology sheet], Floyd 

 County, Georgia. 



Billingsella bivia n. sp. 

 ^ Text figures 65A-C. 



The specimens of this species are preserved in a sandstone and usually occur in the form 

 of flattened casts. The valves are transverse m outline, equally convex, and have their great- 

 est width at the hinge line. The beak of the ventral valve projects over the hinge line and 



FiGxiKE 65.— ijZZmysdia iiora n. sp. A, A', Top and side view of exfoliated dorsal valve, the type specimen, from Locality 14 1, Lower Cambrian,. 

 near Resting Springs, Inyo County, California (U. S. Nat. Mus. Cat. No. 62254a). B, Enlargement (xabout 6) of the outer surface, with strong and 

 flne radiating ribs, otashell from Locality 14p, Lower Cambrian, near Resting Springs, Inyo County, California (U. S. Nat. Mus. Cat. No. 51404). 

 C, Ventral valve from Locality 141, Lower Cambrian, near Resting Springs, Inyo County, California (U. S. Nat. Mus. Cat. No. 52254b). 



is flattened so that it barely rises above the plane of the margins of the shell. The hinge 

 line of the dorsal valve is broadly rounded, and most of the specimens show a fairly well 

 marked mesial sinus. A dorsal valve preserving the outer surface shows it to have been 

 covered by coarse, radiating costae, each of which is marked by a number of minute radiating 

 ridges. 



The species is closely related to Billingsella MgUandensis (Walcott), but differs from that 

 species in being more transverse in outline, m the absence of a concentric striation, and in 

 other details of surface sculpture, and in the prominence of the mesial sinus. 



Formation and locality.— Lower Cambrian: (141) Sandstones about 2,800 feet {853 m.) below the Middle 

 Cambrian in a horizon correlated with No. 2j of the Silver Peal group of the Waucoba Springs section [Walcott, 1908f, p. 



