BracwioroDA. 493 
a well-defined median septum. The spiral ribbon makes but 
few (four or five) volutions; the jugum takes its origin behind 
the middle of the primary lamellz, its lateral branches being 
slightly constricted near their bases ; it is inclined backward in a 
broad curve, the union of the lateral branches taking place at a 
point just within the opposite side of the base of the cones. 
From this point the stem of the jugum is continued as a simple 
process, outward between the coils and almost to the inner sur- 
face of the pedicle-valve. 
_ Type, Ptychospira ferita, von Buch (sp.). Middle Devonian. 
Distribution. Devonian — Lower Carboniferous. 
Uncites, Defrance. 1827. 
(Plate 36, figs. 24-27.) 
Shells usually of large size, elongate-oval or subtriangular 
in marginal outline; valves convex. The pedicle-valve has a 
long and acuminate beak which is frequently distorted and 
always arched or incurved. There is no cardinal area and the 
hinge-line is greatly curved. There is no foramen in mature 
individuals though it may be retained in young forms. The 
deltarium is concave and consists of a single piece, all trace of the 
original components bemg lost. The teeth are supported by 
dental plates and between them lies a broad median ridge which 
narrows as it approaches the hinge. The brachial valve has a 
broad, full beak, which is closely 
incurved and concealed beneath the 
deltarium of the opposite valve. The 
cardinal process is large, erect and 
slightly bilobed on its posterior margin ; 
it rests upon a short plate bearing two 
ridges which are continued into the 
bases of the crura. On either side of 
these ridges and just within the mar- 
gins of the valve is a strong, oval, 
concave, pouch-like plate. The crura 
are very long, passing into the primary f° tshirt hacia rave 
lamellz without interruption The ‘owing cardinal process, marg‘nal 
1 k e pouches, spiral and jugum. (Davip- 
spirals are relatively small, situated soy). 
anteriorly, and consist of seven or eight volutions. These are 
connected by a simple erect jugum, which is situated medially 
100 45 
