SIEBERELLA, Catzer. 
Page 845, 
SIEBERELLA GALEATA, Dalman. 
Fig. 16. Dorsal view of an elongate shell with plicated sinus and smooth lateral 
slopes. 
Fig. 1%. A view of the interior of conjoined valves; showing the spondylium 
and its supporting septum, one of the septal plates and its crural 
process. 
Lower Helderberg group. The Helderbergs, N. Y. 
Figs. 18, 19, Dorsal and profile views of a well-developed example, with trans- 
verse form, highly convex valves, typically developed plicated sinus 
and obscurely plicated lateral slopes. 
Wenlock limestone. Dudley, England. 
SIZBERELLA SIeBERI, von Buch. 
Figs. 20, 21. Dorsal and front views of a typical mature example; showing the 
strong plication of the surface and the sinus in the brachial valve. 
Lower Devonian (Htage F2). Konieprus, Bohemia. (BarR- 
RANDE.) 
GYPIDULA, Hatt. 
Page 846, ; 
GyYPIDULA Ccomis, Owen. 
Fig. 22. Dorsal view of the umbonal region enlarged; showing the longitu- 
dinally striated and sharply delimited cardinal area. 
Upper Devonian. Independence, Iowa. 
Figs. 25, 26. Dorsal and ventral views of a normal example; showing the 
marginal plication of the valves, their convexity and the develop- 
ment of median fold and sinus on pedicle- and brachial valves 
respectively. 
Upper Devonian. Lime Creek, Towa. 
\ 
GypipuLa Romineert, Hall. 
Fig. 23. Dorsal view of the umbonal region of the specimen represented in 
fig. 28, enlarged to show the sharply defined cardinal area and the 
deltidial plates or remnants of the deltidium. » 2. 
Fig. 24. Cardinal view of a pedicle-valve; showing a well-defined cardinal 
area, the teeth and the form of the spondylium. 
Fig. 27. The interior of a brachial valve; showing the curved wall of the 
sessile spondylium. 
Fig. 28. Dorsal view of an individual of ‘average size, with an unusually flat 
brachial valve; showing the cardinal area, plates of the deltidium 
and coarse, irregularly duplicate plication of the surface. 
Hamilton group. Near Alpena, Michigan, 
255 
