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PLATE XIII. 



Page. 

 LlNGULA LONENSiS 108 



Fig. 1. Ventral f valve. 



1 a. Dorsal ? valve. Natural size. 



LlNGULA LuENA 106 



Fig. 2. Ventral valve, from which the surface is largely exfoliated. Natural size. 



LINGULA WHITKI 109 



Fig. 3. Cast of the interior of the dorsal valve, enlarged to two diameters. 



d. Divaricator muscular scar, 

 ad. Adjuster muscular scars. 

 p o. Posterior adductor scar. 

 a a. Anterior adductor scar. 



pp. Supposed area of attachment of the posterior parietal muscle. 

 M M. Supposed area of attachment of the walls of the peri visceral cavity. 

 p 8. Great pallia! sinus. 

 1 8. Lateral branches of the great sinus. 



t. Area, that in another specimen shows the inner ramifications of the great sinus. 

 The various features are rather strongly shown in the figure, but not more 

 so than is justified by the original specimen. 



SKENIDIUM DEVONICUM 116 



Fig. 4. Ventral valve, enlarged to three diameters. 



4 a. Cardinal view, showing the areas of the two valves, the foramen, and the medium 

 septum of the dorsal valve. 



DlSCINA MINUTA '. '. 112 



Fig. 5. View of a rather elongate dorsal valve, enlarged to two diameters. 



STROPHODONTA CALVINI 122 



Fig. 6. View of ventral valve. Natural size. 



STREPTORHYNCHUS CHEMUNGENSIS 117 



Fig. 7. View of a specimen referred to the variety arctostriata. Natural size. 



16. View of a specimen corresponding to the typical forms of the species. Natural size. 



PRODUCTUS SPECIOSUS 133 



Fig. 8. View showing the surface ornamentation and form of the ventral valve. Natural 

 size. 



PRODUCTUS NAVICELLUS 131 



Fig. 9. Lateral view of a somewhat strongly costate variety, enlarged to tfro diameters. 



STROPHODONTA PUNCTULIFERA 121 



Fig. 10. View of ventral valve, showing radiating striae and punctate surface. Natural 

 size. 



STROPHODONTA PERPLANA 120 



Fig. 11. View of a well-preserved ventral valve, with a portion of the outer surface exfoli- 

 ated. 



