PLATE XIII. 



(Figures 1-27 by K. F. Whitkiei.d; 23 hy F. I!. MEKK.emend.) 



Legend. U. Hiiig-e-line. j. Cardinal process. 



D. Deltidiuin. a. Anterior adduclora. 



A. Delthyrium. . a'. Posterior'aciductors. 



t. Teeth. r. Anterior diductors. 



b. Dental sockets. r'. Poateiior diductors. 



s. Median sejjtum. o. Ovarian spaces. 



Genus STROPHEODONTA, Hall. 



Page as4. 

 STROrHEODONTA (BraCHYPKION) PROFUNDA, Hilll. 

 (See Plate XX, tigs. 29-aL) 

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



Fig. 2. A partial cast of a pedicle-valve with the shell removed fiom the upper portidi ; showing the ini- 

 I>re.ssion of the nai-iow area. The margin of the valve preserves the shell with its chai-ai-teris- 

 tic stri^e. 

 Fig. 'A. The central portion of a brachial valve, enlarged from a gutta-per<ha imi)ie.ssion. 



Niagai-a limestone. Racine, Wisconsin. 

 Fig. 4. The interior of a pedicle-valve having the lielthyrium but partially cl():«d, and .sihowing the strong 



crenulations of the cardinal margin neai- the delthyi'ium. 

 Fig. ,"■. An enlargement of the central portiim of the area of the same specimen. X 2. 

 Niagara group. Waldrmi, Indiana. 



Stropheodonta (Brachypkion) naristuiata, Conrad. 



Fig. G. The exterior of the pedicle-valve. 



Fig. 7. The interior of a similar valve. 



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

 tachment of the carilinal process of the opposite vahe. X 3. 



Fig. 9. An eidargement of the centi'al part of the area of another specimen ; showing the char.acter of the 

 deltidium an<l the short row of crenulations. X 3. 



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

 mentation. X 3. 



Fig. 11. An enlaj-gement of a portion of the interior of the pedicle-valve; showing the crenulations of the 



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

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

 Figs. IS, \7). Enlargements of the surface striie. 

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

 Fig. It). An enlargement of one-half of a small pedicle-valve ; showing the fasciculate stria>. 



Lower Helderberg group (Tentaculite and Pentamerus limestones). SchoharleCo., N. Y. 



Stropheodonta varistriata, var. arata, Hall. 



Figs. 17, 18. Views of two pedicle-valves ; showing the strongly fasciculate surface striie. 

 Lower Helderberg group. Becraft's M<nmtaiv. Hudson, N. ¥. 



Stropheodonta profunda ? 



Figs. 19, 20. Views of a specimen which has heen referred, with doubt, to this spe<:ies. 

 Clinton grouji. Niagara county, N. Y. 



Stropheodonta varistriata, Conrad (= 8. impressa, Conrad). 



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

 region. 



Lower Helderberg group. Eastern New York. 



