Fig. 
Figs. 
Fig. 
Figs. 
Fig. 
Fig. 
Fig. 
Fig. 
Figs. 
Fig. 
PLATE LX.XII—Continued. 
21. Dorsal view of a somewhat elongate shell, with full, prominent umbo, and destitute of surface 
plications. 
Upper Devonian. Lime Creek, Iowa. 
22, 23. Front and profile views of a more orbicular shell, alst' without plications. Should the smooth 
shells, now included under this name, be found to jn esent permanent differences from the pli¬ 
cated forms, they may be termed Cfypidula laevis. 
Upper Devonian. Independence, Iowa. 
24. The interior of the umbonal jiortion of conjoined valves; showing, above, the free spondylium of 
the pedicle-valve, and, beneath, the sessile spondylium of the brachial valve. 
Silicious beds, probably of the age of the Hamilton group. Central Indiana. 
Gypidula l^viuscula, Hall. 
25, 26. Dorsal and profile views of an average specimen ; showing the smooth, evenly convex valves 
and the almost complete obsolesence of fold and sinus. 
Upper Devonian. Lime Creek, Iowa. 
Gypidula Romingeri, sp. uov. 
27. Cardinal view of a pedicle-valve ; showing a well defined cardinal area, the teeth and the form of 
the spondylium. 
28. Dorsal view of the umbonal region of the specimen represented in fig. 30, enlarged to show the 
sharply defined cardinal area and the deltidial plates or remnants of the deltidium. X 2, 
29. The interior of a brachial valve ; showing the curved walls of the sessile spondylium. 
30. 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 jolication of the surface. 
31. 32. Dorsal and profile views of a large specimen with a finer and more regular surface plication, 
more conspicuous and deeply incurved ventral umbo and clearly defined sinus on the brachial 
valve. The shell is largely exfoliated over the brachial valve, exposing the broken base of the 
spondylium and the genital markings aboiit it on the surface of the cast. 
33. The interior of a large brachial valve ; showing the form and extent of the spondylium. 
Hamilton group. Near Alpena, Michigan. 
I 
