BRaAcHIOPODA. 903 
Eichwaldia, Billings. 1858. 
(Plate 54, figs. 12-22.) 
Shells subtriangular in outline, with biconvex valves, the 
pedicle-valve having a broad median sinus, and the brachial valve 
a corresponding median fold. The umbo of the pedicle-valve is 
acute and arched over the opposite valve, though not closely 
appressed against it. As far as has been ascertained, the umbonal 
space between the two valves is open, that is, there is no del- 
tidium or pair of deltidial plates extending from the apex down- 
Fie. 662, 
Hichwaldia reticulata, Hall. 
Fie. 659. Dorsal view. Fia. 663. Interior of brachial valve. 
Fie. 660. Cardinal view. Fie. 664. Vertical section of shell. 
Fie. 661. Longitudinal section of two valves. Fie. 665. Enlargement of the surface. 
Fia. 662. Interior of pedicle-valve. 
Notation: f, “bare spot” or foramen; P(e), deltidium or internal plate; c’, umbonal surface 
of pedicle-valve; tT, teeth; B, dental sockets; J, cardinal process; s, median septum of brachial 
valve. 
ward ; but there is a short triangular plate or diaphragm which 
begins at the apex of this valve and extends forward beyond the 
posterior edge of the brachial valve, and thus serves the purpose 
of the deltidium, though deeply depressed within the cavity of 
the pedicle-valve. This diaphragm is usually quite short and 
confined to the apical region, but it may extend for fully one- 
fifth the length of the valve, its anterior margin being free and 
its lateral margins adherent to the inner cardinal slopes. The 
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