PLATE LXXII. 



(Figurea 1-3, 18-20, 22, 23 by R. P Whitfield; 4, 5 copies; 6-9, 24, 27-33 by E. Emmons; 10-14 by F. B. Meek; 1&-17, 21, 25. 



26byG. B. Simpson.) 



Genus SIEBERELLA, CEhlert. 



Page 241. 



SlEBERELLA NUCLEUS, Hall .iikI Whitfield. 



Figs. 1-3. Dorsal, profile and front views of the orig-inal specimen ; showing the form of the shell and the 

 strong plication in the median sinus 



In limestone of the age of the Clinton gi-oup. Near Louisville, Kentucky. 



SlEBERELLA SlEBERI, VOll Bucll. 



Fijfs. 4, 5. Doraal 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). Koniepras, Bohemia. (After Barrandb.) 



SlEBERELLA RoEMERi, iioiii. iiov. (^Pen(aineiu.<i galealus, F. Koemer). 



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 Silunan. Perry county, Tennessee. 



SlEBERELLA GALEATA, DillniiUl. 



Figs. 7, 8. Dorsal and profile views of a well-developed example, with transveree 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 j showing the fine, irregularly anas- 

 tomosing concentric raised lines. 



■Wenlock limestone. Dudley, England. 



Fi^. 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 sujjporting septum, 

 one of the septal plates and its crural ) rocess. 



Fig. 13. Cardinal view of a lai-ge internal cast of both valves ; showing the cavities left by the spondyl- 

 ium and septum in the pedicle-valve, and by the septal i lates in the brachial valve ; also the 

 genital markings in the umbonal region of the pedicle-vaive. 



Lower Helderberg group. T/u; Helderbergs, New York. 



SlEBERELLA 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 group (Upper Pentamerus limestone). The Helderbergs, New York. 



Genus GYPIDULA, Hall. 



Page 241. 



Gypidula comis, Owen. 



Fiire 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 respectively. 



Upper Devonian. Lime Creek, Imca. 

 Fiire 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 Devonian. iTidependence, Iovm. 



