PLATE XIII. 



(Figures 1-27 by K. P. Whitfielb; 28 by F. B. Meek, emend.i 



Legend. H. Hing-e-litie. j. Cardinal proues.?. 



D. Deltidium. a. Anteiior adductora. 



^. Delthyi'ium. a'. Posteiior'adductorp. 



t. Teeth. r. Anteidoi' diductors. 



b. Dental sockets. r'. Posteiioi' dirtuctoi-s. 



s. Median septum. o. Ovarian spaces. 



Genus STROPHEODONTA, Hall. 



Page 284. 



Stropheodonta (Brachypkion) profunda, Hall. 

 (See Plate XX, figs. 29-31.) 

 Pig. 1. The internal cast of a pedicle-valve ; showing the muscular impressions. 



Fig. 2. A partial cast of a pe(]i(-le-valve with the shell removed from the upper portion ; showing the im- 

 pression of the narrow area. The margin of the valve presei-ves the shell witli its characteris- 

 tic striae. 

 Pig. 3. The centi-al portion of a brachial valve, enlarged from a gutta-percha imjiression. 



Niagara limestone. Racine, Wisco9igin. 

 Fig. 4. The interior of a pedicle-valve having the delthyrium but partially closed, and .showing the strong 



ci'enulations of the cardinal margin near the delthyrium. 

 Fig. f>. An enlai'gement of the central portion of the area of the same specimen. X 2. 

 Niagara group. Waldron, Indiana. 



Stropheodonta (Brachyprion) vauistriata, Conrad. 



The exterior of the pedicle-valve. 

 The interior of a similar valve. 



An enlargement of a. poi'tion of the same specimen ; showing the lo'eaking of the area by the de- 

 tachment of the cardinal process of the opposite valve. X 3. 

 9. An enlai'gement of the central part of the area of another specimen ; showing the character of the 

 deltidium and the short row of crennlations. X 3. 

 An enlargement of the nmbonal portion of a pedicle-valve; showing the character of the orna- 

 mentation. X 3. 

 An enlargement of a poi'tion of the interior of the pedicle-valve ; showing the crenulations of the 



hinge and the character of the muscular impressions. X 2. 

 The cardinal process and crnral plates. X .2. 

 Figs. 13, 15. Enlargements of the sui'face stri«. 

 Fig. 14. The exterior of a pedicle-valve. 

 Fig. 16. An enlargement of one-half of a small pedicle-vsilve ; showing the fasciculate striae. 



Lovfer Helderberg group (Tentaculite and Pentamerus limestones). Schoharie Cu., N. T. 



Stropheodonta varistriata, var. arata, Hall. 



Figs, n, IS. Views of two pedicle-valves ; showing the strongly fasciculate surface stris. 

 Lower Helderberg group. Becraft's Mmmtain, Hudson, N. Y. 



Stropheodonta profunda ? 



Figs. 19, 20. Views of a specimen which has heeii referi'ed, with doubt, to this species. 

 Clinton group. Niagara comity, N. Y. 



Stropheodonta varistriata, Conrad (= *S'. imjjressa, Conrad). 



Figs. 21, 22. Two views of this shell; showing the depressed umbo and the great convexity in the pallial 

 region. 



Lower Helderberg group. Eastern New York. 



Fig. 

 Fig. 

 Fig. 



U. 



7. 

 8. 



Fig. 



9. 



Fig. 



10. 



Fig. 



11. 



Fig. 



12. 



