PLATE LXXII. 



(Kigures 1-3, IS-20. 3J, ii by 11. P WHITFIELD; 4, 5 copies; li-9, -^4. 27-33 by E. Emmoss; 10-U by F. B. Meek; 15-17, 21, Jfl, 



21) by G. K. Simpson.) 



Genus SIEBEKELLA, CEhlert. 



I'age 241. 



SlEBERELLA NUCLEUS, Hilll Uiul Wllltficld. 



Figs. 1-3. Doraal, profile and iVont views of the oritfinal specimen ; showing- the form of tlic shell and the 

 strong plication in the median sinus 



In limestone of the age of the Clinton group. Near LouisviUe, Kentucky. 



SlEBERELLA SlEBEKL VOll Bllcll. 



Figs. 4, 5. Dorsal and front views of a typical mature example ; showing the strong plii'ation of the sur- 

 face and the sinus in the bi'achial valve. 



Lower Devonian (Etage Fa). Koniepriis, Bohemia. (After Bakhande.) 



SlEBERELLA RoEJiERi, uoiii, iiov. (Penknueiu.'i ffcdecUm, F. Roeiuci). 



Fig. 6. Dorsal view of an individual of rather large size ; .showing the characteristic plication of tlie sinus 

 and lateral slopes aViout the margin, and their obsolescence in the umtjonal i-egion. 

 Upper Silurian. Perry county, TetiTiessee. 



SlEBERELLA GALEATA, Dulnillil. 



Figs. 7, 8. Dorsal and profile \-iews of a well-developed example, with transverse form, highly convex 

 valves, typically developed plicated .sinus and obscurely plicated lateral slopes. 



Fig. 9. An enlargement of the external surface of the same specimen ; showing the tine, irregularly anas, 

 tomosing concentric raised lines. 



Wenlock limestone. Dudley, England. 



Figs. 10, 11. Profile and dorsal views of an elongat^; shell with plicated sinus and smooth lateral slopes. 



Fig. 12. A view of the interior of conjoined valves ; .showing the spondylium and its sujiporting septum, 

 one of the sejital plates and its crural j. rocess. 



Fig. 13. Cardinal view of a large intei-nal cast of both valves ; showing the cavities left by the spondyl- 

 ium and septum in the jiedicle- valve, and by the septal \ lates in the brachial valve; also the 

 genital markings in the umlxmal region of the pedicle-vane. 



Lower Helderberg group. Tfte HeUlei'berg.f, Nexo York. 



SlEBERELLA PSEUDOCiALEATA, Hall. 



Fig. 14. Profile view of a typical specimen ; showing the absence of surface plications. Tlie representa- 

 tion of radial lines in the drawing is erroneous 



Lower Helilerberg gr<iup (Upper Pentaraerus limestone). The Hetderhergs, 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 pediide and brachial 

 valves respectively. 



Upper Devonian. Lhiie Creek, Imm. 

 Figs. 18, 19. -Dorsal and cardinal views of a plicated specimen which retains a well defined cardinal area. 

 Fig. 20. Dorsal \'iew of the nmbonal region enlarged ; sho\ving the longitudinally striated and sharply 

 delimited cardinal area. 



Upper Devonian. IndependeJice, Iowa. 



