BRACHIOPODA. 167 
as in Murista, but as a rule the ribbon makes fewer (from six to 
twelve) volutions at maturity. The jugum is simple, the branches 
being more nearly erect than in Mertsta, MurisTexra, etc., and 
SSS 
Fias. 302, 303.—The jugum of Whitfieldella nitida, Hall. 
' beyond their junction continued into a short, acute, generally 
slightly curved process, which makes a large angle with the 
direction of the lateral branches. The muscular impressions, 
which are very faint, are divided, longitudinally, by the median 
septum, and transversely, into anterior and posterior scars. 
From the ante-lateral margins of the muscular area in both valves 
radiates a series of vascular sinuses, the principal trunks of which 
are very conspicuous; this feature, however, is rarely retained. 
External surface of the valves smooth or concentrically striate. 
Shell-substance fibrous, impunctate. 
Type, Whitjieldella nitida, Hall, (sp.). Niagara group. 
Distribution. Upper Silurian — Lower Devonian. 
Hyattella, Hall. 1893. 
(Plate 32, figs. 10-17.) 
Shell compactly subpentahedral; the umbo of the pedicle-valve 
acute, concealing most of the deltidial covering. The pedicle- 
valve bears a strong median sinus and two 
faint lateral sinuses, the opposite valve 
having corresponding folds. The surface pene 
of the shell and the ante-lateral margins 
are deeply sinuate. Fine, sharp, closely Tat ae OPE 
crowded concentric striz cover the exterior. ella congesta, Conrad. 
The interior of the pedicle-valve has a deep and strongly striate 
pedicle-cavity, bounded by strong dental lamella; the diductor 
scars are distinctly defined, inclosing a linear adductor. In the 
brachial-valve the hinge-plate is triangular and divided medially 
by a deep cleft. The lateral portions are broad and elevated, 
19 
