i 



PLATE XIII. j 



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



Legend. II. Hinge-liiie. j. Caidiiial process. 



U. Deltidinin. ^- Anterior adductors. 



^. Delthyrium. , »'■ Posterior'adductors. 



t. Teeth. I'. Anterior diductors. 



b. Dental socket.«. '■'. Posterior diductors. 



s. Median sejituni. o. Ovarian spaces. 



Genus STEOPHEODONTA, Hall. i 



P.ige 284. _ ! 



Stropheodonta (Brachypkion) profunda, Hull. I 



(See Plate XX, figs. 29-31.) 1 



Fig. 1. The internal cast of a pedicle-valve ; showing the muscular impiessions. : 



Kig. 2. A partial cast of a pedicle-valve with the shell removed fr-om the upper portion ; showing the im- , 



pi-e.ssion of the nariow ai-ea. The margin of the valve (ireserves the shell with its characteris- ' 



tic sti'iie. I 



Fig. :i. The central portion of a brachial valve, enlarged from a gutta-percha impiessioii. ] 



Niagara limestone. Racine^ Wisconsin. 

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



crennlations of the cardinal margin near the delthyrium. 



Fig. .">. An enlargement of the central portion of the area of the same specimen. X 2. ^ 



Niagara group. Waldron, Indiana. \ 



i 



Stropheodonta (Brachyprion) varistriata, Coiimd. 



Fig. tj. The exterior of the jiedicle-valve. \ 



Fig. 7. The interior of a similar valve. i 



Fig. 8. An enlargement of a portion of the same specimen ; showing the breaking of the area by the de- 

 tachment of the cardinal pi'ocess of the opposite valve. X 3. 



Fig. 9. An enlargement of the central part of the area of another specimen ; showing the char.acter of the 

 <leltidiuni and the short row of crennlations. X 3. 



Fig. 10. An enlargement of the umbonal portion of a pedicle-valve; showing the character of the orna- 

 mentation. X 3. 



Fig. 11. An enlargement of a portion of the interior of the jiediirle- valve ; showing the crennlations of the 

 hinge and the charactei' of the muscular impressions. X -. 



Fig. 12. The cardinal process and crural plates. X 2. 



Figs. 13, 1!). Enlargements of the surface stria>. 



Fig. 14. The exterioi' of a pedicle-valve. 



F\g. 16. An enlargement of one-half of a small pe<licle-valve ; showing the fasciculate stna>. ' 



Lower Helderberg grouji (Tentacnlite and Pentamerns limestones). SchofiarieCii., N. Y. 



1 



Stropheodonta varistriata, var. arata, Hall. , 1 



Kig.s. 17, IS. Views of l\»o peilicle-valves ; showing the strongly fasciculate surface stria'. J 



Lower Helderberg group. Becraft's Mountain, Hudson, N. Y. 1 



Stropheodonta profunda ? ■ 



Figs. 19, 20. View.s of a .specimen which has heen referred, with doubt, to this species. 

 Clinton gi'onp. Niagara comity, N. Y. 



Stropheodonta varistriata, CoiujkI (= ,Sf. /mpressa, Conrad). j 



Figs. 21, 22. Two views <if this shell ; .slnivving the clepressed umbo and the great convexity in the pallial ■ 



region. " j 



T^owcr Helderberg grouj). Eastern New Yorlc. ■ I 



