PLATE LXXII. 
(Figures 1-3,18-20, 22, 23 by R. P. Whitfield; 4, 3 copies; 0-9, 24, 27-33 by E. Emmons; 10-14 by P. B, Meek; 15-17, 21, 25, 
'20 by G. B. SiMPSON.) 
Genus SIEBERELLA, CEhlert. 
Page 241. 
SiEBERELLA NUCLEUS, Hall aiicl Whitfield. 
Figs. 1-3. Dorsal, profile and front views of the original specimen ; showing the form of the shell and the 
strong plication in the median sinus. 
In limestone of the age of the Clinton group. Near Louisville, Kentuclty. 
SlEBKRELLA SlEBERI, VOll Bucll. 
Figs. 4, 5. Dorsal and front views of a typical mature example; showing the strong plication of the sur¬ 
face and the sinus in the brachial valve. 
Lower Devonian (Etage Fj). Konieprus, Bohemia. (After Barrande.) 
SiEBERELLA Roemeri, iioiii. iiov. [Peiitauierus galeatus, F. Roeiner). 
Fig. 6. Dorsal view of an individual of rather large size ; showing the characteristic plication of the sinus 
and lateral slopes about the margin, and their obsolescence in the umbonal region. 
Upper Silurian. Perry county, Tennessee. 
SiEBERELLA GALEATA, DllliniUl. 
Figs. 7, 8. Dorsal and profile views of a well-developed example, with transverse form, highly convex 
valves, typically developed plicated sinus and obscurely plicated lateral slopes. 
Fig. 9. An enlai’gement of the external surface of the same specimen; showing the fine, irregulaily anas¬ 
tomosing concentric raised lines. 
Wenlock limestone. Dudley, England. 
Figs. 10, 11. Profile and dorsal views of an elongate shell with plicated sinus and smooth lateral slopes. 
Fig. 12. A view of the interior of conjoined valves ; showing the spondylium and its supporting septum, 
one of the septal plates and its crural} rocess. 
Fig. 13. Cardinal view of a large internal cast of both valves; showing the cavities left by the spondyl¬ 
ium and septum in the pedicle-valve, and by the septal plates in the brachial valve; also the 
genital markings in the umbonal region of the pedicle-vaive. 
Lower Helderberg grouj). The Helderhergs, New York. 
SiEBERELLA PSEUDOGALEATA, Hall. 
Fig. 14. Profile view of a typical specimen; showing the absence of surface plications. The representa¬ 
tion of radial lines in the drawing is erroneous. 
Lower Helderberg grouj) (Upper Pentamerus limestone). The Helderhergs, New York. 
Genus GYPIDULA, Hall. 
Page 241. 
Gypidula comis, Owen. 
Figs. 15-17. Dorsal, ventral and profile views of a normal example ; showing the marginal plication of the 
valves, their convexity and the development of median fold and sinus on pedicle and brachial 
valves resiiectively. 
Upper Devonian. Lime Creek, lo^va. 
Figs. 18, 19. - Dorsal and cardinal views of a plicated specimen which retains a well defined cardinal area. 
Fig. 20. Dorsal view of the umbonal region enlarged; showing the longitudinally striated and sharply 
delimited cardinal area. 
Upper Dev.onian. Lndependence, Iowa. 
