844 Report OF THE STATE GEOLOGIST. 
vertical septa, and extend for some distance in front of them. 
They are divided by a low axial ridge. 
Shell-substance fibrous, impunctate. 
Type, Conchidium biloculare, Linné (—Gypidia or Pentamerus 
conchidium, Dalman et al. Upper Silurian limestone, Gotland.) 
Distribution. Upper Silurian — Devonian. 
Pentamerus, Sowerby. 1813. 
(Plate 47, figs. 1-9.) 
Smooth shells, of variable contour, sometimes bearing a few 
broad and obscure radiating undulations. There is no median 
fold and sinus, though a median prolongation of the valves, 
defined by two divergent lateral furrows, is a normal character. 
A concave deltidium is sometimes retained, and a faint lobation 
— 
Fig. 453. Fia. 454. Fia. 455. Fia. 456. 
Fig. 453. Pentamerus oblongus, Sowerby. A transverse section, showing the septa. 
Figs. 454, 455. Transverse sections of the septa of Pentamerus oblongus. Fig. 454 shows the 
septum of the pedicle-valve and the inclosure of its base by the shell-substance 
of the valve. Fig. 455 is an enlargement of the septa of the brachial valve, and 
shows a thin coating of testaceous matter upon ths inner faces of the prismatic 
walls. 
Fig. 456. Pentamerus cylindricus, Hall. A transverse section, showing the septa. 
of the apical end of the spondylium is the sole evidence of a car- 
dinal process. The depth of the spondylium and septal cavity 
varies with the convexity of the valves. Sometimes the septa 
unite before reaching the inner surface of the brachial valve and 
the spondylium thus formed is supported by a low axial septum. 
Type, Pentamerus oblongus, Sowerby. i 
Distribution. Upper Silurian — Lower Devonian. 
Barrandella, Hall. 1893. 
Synonym; Clorinda, Barrande, 1879. 
(Plate 48, figs. 1-5.) 
Galeatiform pentameroids with median fold on the brachial 
valve and median sinus on the pedicle-valve. Shells small, sur- 
face smooth or rarely plicate. 
96 
