EXPLANATION OF PLATE XVI. 

 Saxicava bilineata Conrad (p. 93). 



Figs. 1, 2. Exterior natural size and enlarged interior view of a short broad form. 

 3. View of an imperfect right valve of an elongate form = S. rut/osa L. 



Saxicava my^eformis Conrad (p. 90). 

 Figs. 4, 5. Exterior of the shell, natural size, and enlargement of the hinge. Type specimen. 



Saxicava parilis Conrad (p. 92). 

 Fig. 6. View of the type specimen, natural size. 



Periploma alta Conrad (p. 85). 



Figs. 7. Exterior view of a specimen, showing the imprint of the internal rib on the right of the 

 beak. 

 8. Interior of Conrad's type specimen, showing hinge structure. 



Mya panop^a Goldfnssi (p. 89). 



Figs. 9, 10. Exterior and interior views of the best valve obtained ; the hinge broken. 



11. Hinge of a fragment of a left valve. 



12. Hinge of a right valve, looking parallel to the plane of the valve. 



13. Hinge of a right valve; the tooth broken away at a. 



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