BRAcHIOPODA. 853 
Shell-substance finely punctate. 
Surface smooth or covered with fine concentric strizw, accom- 
panied by stronger wrinkles of growth. The inner lamin are 
sometimes marked by obscure radiating striz near the margins 
of the valves. 
Type, Mewberria Johannis, Hall. 
Distribution. Middle Devonian. 
Centronella, Billings. 1859. 
(Plate 52, figs. 1-7.) 
Shells plano-convex or concavo-convex. Pedicle-valve with 
acute incurved beak, perforated at its extremity, the foramen 
being continuous with a partially closed delthyrium; medially 
ridged, and with abruptly sloping sides. On the interior the 
teeth are large, thick at their extremities and adherent to the 
lateral walls of the shell. Between them is a deep pedicle-cavity, 
in the bottom of which lie the elongate scars of the adductor 
muscles, and about their anterior portion the small, flabellate 
diductors. 
The brachial valve is very shallow, rendered concave exteriorly 
by a median sinus which does not make itself apparent on the 
interior. Beak small, apex not incurved. Dental 
sockets broad, bounded interiorly by the high walls 
of the hinge-plate. This plate is divided medially 
by a deep furrow extending to the apex, and, there- 
fore, consists of two processes which are elevated, 
thickened and rest on the bottom of the valve. yg 42 cen. 
From the anterior face of these arise the crura tronella glans. 
which converge for a short distance, and expand to eee ee yee 
form two broad, acute jugal processes. From here showing the 
the lateral branches of the brachidium curve out- tess 
ward, gradually turning from a vertical to a horizontal position, 
broaden rapidly and unite to form an anterior triangular plate 
which bears a median ridge, where the two lateral branches 
are conjoined. The whole of the anterior portion of the brach- 
idium is inclined gently upward toward the cavity of the opposite 
valve. 
105 
