PLATE XII. 



(Figures 1-S, 8-21 by K. f. Whiiuki.k; b, 7 by F. It. JIkek.) 



Legend. H. Hiuge-line. b. Dental sockets. 



[D. Deltidium, jiedicle- valve. t. Teeth. 



C. Deltidium, brachial valvn. a. Aiiterioi- aildiictors. 



a. Cardinal area, outer i)ortion. a'. Posterior adductors, 



j. Cardinal process. r. Diductoi-s. 



i. Lobes of cardinal process. 



Genus STROPHONELLA, Hall. 



Pape 290. 



StROPHONELLA ( ) STRIATA, Hall. 



Fig. I. The exterior of a brachial valve 



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



the muscidar area, and the rrennlations of the cai-dinal mai-gin near the delthyrium. 

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

 crenulafed margin, and the deltidium enveloping the lower portion of the lobes of the cardinal 

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

 to the line of vision ; the groove between the lobes of the canliiial process is, therefore, much 

 foreshortened, and made to appear shallow ; the crural i-idges are also to be regarded as re- 

 treating rapidly into the background. 



Niagara grouii. Waldron, Indiana. 



Strophonella semifasciata, Hull. 



Fig. 4. The exterior of the concave pedicle-valve. 



Fig. 5. An enlargement of the centi'al poilion of the area of both valves; showing the development of 



the deltidia and the oblicjue striie on the broad triangular space enclosed by the lines a. a, a. 



[This space should be detined by lines extending from the apex to 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. 



Fig. tj. The exterioi' of a brachial valve. 



Fig. 7. A i)rofile of the same ; showing the concavity in early gi'owth-stages, followed by great convexity 

 and strong genicnlation. 



Fig. 8. The interior of the brachial valve ; showing the creiiulations of the cardinal margin, the cardinal 

 process, slightly developed crural plates, and the addnctoi' impi'e.ssions. 



Fig. 9. The interior of the pedicle-valve ; showing the crenulations of the hinge-margin, the closed del- 

 thyrium, and the arrangement of the mu.=cular scars. 



Lower Helderberg gi-oup. Albany cmmty, N. Y. 



Strophonella punctulifera, Conrad. 



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



pallial region. 

 Fig. 11. An internal cast of a brachial valve ; showing the muscular imiirints and the crenulations in the 



matrix left by the removal of the hinge. 

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



delthyrium in each valve. X 1^. 



Lower Helderberg group. Near Clarksville, N. T. 



Strophonella ampla, Hall. 



Fig. 13, An internal cast of a pedicle-valve; showing the muscular impressions and marks of the strongly 

 pustulose interior surface. In the inipi'int left by the c-ardinal ai-ea 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 inteiior of a pedicle-valve in which external evidence of the deltidium is lost and the crenula- 

 tions of the hinge extend more than half the length of the area. The margin of the area on 

 each side of the deltidium has been broken away by the detachment of the <!arilinal process of 

 the other valve. 



Corniferons limestone. Oiunidaga Valley, iV. Y. 



Fig. 1.1. An enlargement of the sui'face strise. 



