PLATE XII. 



(Figures J-5, 8-21 by It. f. WaiTiiiii^Di i., 7 by F. B. MEEK.) 



Leg-end. H. Hinge-liue. b. Dental sockets. 

 [D. Deltidiuni, pedicle-valve. t. Teeth. 



C. Deltidium, brachial valve. a. Atiteiioi- adductors. 



a. Cardinal area, outer portion. a'. Posterioi- addiictoi-s. 

 j. Cardinal process. r. Didnctors. 



i. Lobes of cardinal process. 



Genus STROPHONELLA, Hall. 



Page 290. 

 StROPHONELLA ( ) STRIATA, Hall. 



Fig. 1. The exterioi- of a brachial valve. 



Fig. 2. The interior of a pedicle-valve ; showing the extension of the dental lamellae along the sides of 

 the muscular area, and the crenulations of the cardinal margin near the delthynum. 



Fig. 3. An enlargement of the central portion of the brachial valve ; showing the cardinal area, its 

 O'enulated margin, and the deltidiuni enveloping the lower jjortitm of the lobes of the cai-dinal 

 process. In this drawing the specimen is viewed with the cardinal area nearly at right angles 

 to the line of vision ; the gi'oove between the lobes of the cardinal pi-ocess is, therefore, much 

 foi'eshortened, and made to appear shallow ; the crinal i-idges are also to be regarded as I'e- 

 treating rapidly into the background. 



Niagara group. Waldrmi, Bulimia. 



Stuophonella semifasciata, Hall. 



Fig. 4. The exterior of the concave i]edicle-valve. 



Pig. b. An enlargement of the central poi-tion of the area of both valves ; showing the development of 



the deltidia and the oblique sti-ite on the liroad triangular space enclosed by the lines a, a, a. 



[This sjiace should be detined l)y lines extending from the apex t<i the limit of the figure on 



each side, and which may be obscure in some of the figures.] 

 Niagara group. Waldron, Indiana. 



StROPHONELLA Leavenworthana, Hall. 



The exterioi- of a brachial valve. 



A protile of the same ; showing the concavity in early growth-stages, followed by great convexity 



and sti'ong geniculation . 

 'J'he interior of the brachial valve ; showing the crenulations of the cardinal margin, the cardinal 



process, slightly develoiied crural plates, and the addnctoi- impres.'^ions. 

 The interior of the pedicle-valve ; showing the crenulations of the hinge-margin, the closed del- 



thyrium, and the ari'angement of the muscular scars. 



Lower Helderberg group. Albany cmmty, N. T. 



StROPHONELLA punctulifera, Coiiracl. 



Fig. 10. The exteiior of the brachial valve; showing the concavity in the umbonal, and convexity in the 



pallial region. 

 Fi"'. 11. An internal cast of a brachial valve ; showing the muscular imprints and the crenulations in the 



matrix left by the removal of the hinge. 

 Fig. 12. The cardinal areas of both valves of fig. 10 ; showing the narrow convex deltidium closing the 



delthyrium in .each valve. X IJ- 



Lowei' Helderberg group. Near Clarltsville, N. T. 



StROPHONELLA AMPLA, Hall. 



Fiu\ 13. An internal cast of a pedicle-Vidve ; showing the muscular impressions and marks of the stronglj' 

 pnstulose interior sui'face. In the imprint left by the cardinal area are seen the crenulations 

 of the hinge-line, and the mark of the small, linear convex deltidium. 

 Schoharie grit. Albany county, N. Y. 



Fig. 14. The interior of a pedicle-valve in which external evidence of the deltidium is lost and the crenula- 

 tions of the hinge extend moi'e than half the length of the area. The margin of the ai-ea on 

 each side of the deltidium has been b]-oken away by the detachment of the cai-dinal process of 

 the other valve. 



Coniiferous limestone. Owmdaga Valley, N. T. 



Fig. 15. An enlargement of the surface striae. 



Fig. 



6. 



Fig. 



7. 



Fig. 



8. 



Fig. 



9. 



