PART I CHAZYAN AND RELATED BRACHIOPODS—COOPER 767 
more, considerable uniformity of size has been observed in B. immatura. For 
these reasons it is preferred to regard the numerous specimens of this form in 
the collection as a distinct species. 
In addition to B. immatura two other species like it are known: One from 
the Mystic conglomerate of Quebec, the other, B. siphonata, from the Pratt 
Ferry formation of Alabama. The former species, B. matutina, has a much more 
elevated umbo than the Effna form. Its interior is unknown, and it is possible 
that the species may not be related generically to Bimuria. The Alabama species 
differs in its slender, transverse outline. 
BIMURIA LAMELLOSA (Bassler) 
Plate 194, A, figures I-10; plate 212, A, figures I-10 
Christiania lamellosa Basster, Cambrian and Ordovician: Maryland Geol. Surv., p. 257, 
pl. 49, figs. 3-10, 1919.—Butts, Virginia Geol. Surv. Bull. 52, p. 109, pl. 95, figs. 7-10, 
I . 
C sae trentonensis brevis Butts, idem, fig. 1. 
Shell small for the genus, wider than long with the greatest width slightly 
anterior to the hinge. Cardinal extremities narrowly rounded. Lateral margins 
gently rounded ; anterior margin broadly to narrowly rounded. Umbonal region 
of both valves smooth; remainder of surface marked by more or less distant 
concentric lamellae. Exfoliated shells appear to be smooth. 
Pedicle valve strongly convex in lateral profile with the greatest convexity 
at about the middle. Anterior profile forming a semicircle. Umbo swollen; 
beak small, drawn into a sharp point. Foramen minute, located slightly posterior 
to the apex of the beak. Valve strongly inflated with steep lateral and postero- 
lateral slopes. Fold poorly defined, developed only in median region and near 
the front. Interarea curved, strongly anacline. 
Brachial valve deeply concave with the greatest concavity about at the middle. 
Anterior to the middle a low, not well defined sulcus indents the commissure 
toward the brachial valve. Interarea well developed, hypercline to orthocline. 
Notothyrium closed by a thick and large chilidium. 
Brachial processes widely divergent, thin, defining deep sockets for the teeth. 
Cardinal process a simple ridge, nearly obsolete and poorly defined in the 
extreme posterior part. A low ridge extends anterior to the rudimentary process 
nearly to the anterior margin. This ridge is highest at the place where the 2 
divergent septa originate and extends between them. Outside each septum is 
a papillose lobate area on the posterior portion of which the adductor muscles 
were attached. The outside of these lobate areas is elevated above the floor of 
the valve. 
Measurements in mm.— 
Brachial Hinge 
Length length width Width Thickness Height 
THectotype "snc fn. cae 10.4 WEG Liey, 10.9 2.2 5.2 
Paratype (66168c).... 10.7 8.1 11.9 10.0 2.5 4.6 
