BRAOHIOPODA. 829 
to that of Hypornyris; the median septum of the brachial valve 
is extremely faint when present, but is usually undeveloped. 
Muscular impressions not large but well defined and clearly 
subdivided. Vascular sinuses sometimes retained on the pedicle- 
valve, always obscure on the brachial valve. 
(Type, Pugnax acuminatus, Martin. Devonian—Carboniferous.) 
Eatonia, Hall. 1857. 
(Plate 44, figs. 30-40.) 
Concavo-convex shells with median fold and sinus, and plicated 
or radiate-lineate exterior. Anterior margin deeply sinuate. 
From the beak of the pedicle-valve diverge two lateral cardinal 
ridges which limit a more or less distinct false area. On the 
interior the teeth are adnascent to the lateral walls of the valve, 
all traces of supporting lamellae being absent. Muscular area 
large, flabellate and deeply excavated in the substance of the 
shell. Pedicle-impression broad, traversed medially by a longi- 
tudinal groove; diductors extending for about one-half the length 
of the shell, their outer margins being elevated; they enclose a 
pair of small central adductor scars whose posterior margins are 
raised into prominent myophores. The scars are divided by a 
slight median septum which is continued posteriorly ; this septum 
being often rendered very conspicuous by the growth of the shell 
about the apophyses of the cardinal process of the opposite valve, 
and in the extreme cases its development is such that it rises 
above, and incloses the adductor scars, the latter being excavated 
in its substance. 
In the brachial valve the dental sockets are long and narrow, the 
* cardinal process very large and composed of a stout, erect stem 
resting upon a rather short median septum, and divided at its 
summit into two long, divergent, tooth-like branches, whose 
upper faces extend to the interior surface of the opposite valve; 
hence their greatest elevation is at their anterior extremities, 
whence they slope toward the beak of the valve, usually uniting 
before that point is reached. The surface of attachment of each 
of these apophyses is medially grooved. Below them, and at the 
base of the central stem, arise the crura, which are long, straight 
and slender, with expanded extremities. The muscular scars are 
clearly defined and consist of a pair of small posterior adductors, 
81 
