PLATE 18. 



Page 

 Fig. 1. Strophodonta nacrea 104 



1 a, b, c. Ventral valves of this species, showing varieties of form. 



1 d. A dorsal view of lig. 1 c. 



1 e. A profile of the same. 



1/. A profile view of 1 a. 



1 g. Interior of the ventral valve. The open deltidium is due to accident. 



1 k. The interior of a dorsal valve. 



Fig. 2. Strophodonta inequistriata 106 



2 a, b, c. Dorsal views of three individuals, showing the extremes of the ordinary forms. 

 2 d, e,f. Ventral views of the preceding specimens. 



2g. A profile of fig. 2 6. 

 2 h. The interior of a dorsal valve. 

 2 t. The interior of a ventral valve. 



2 k. The interior of a ventral valve enlarged to two diameters, showing the peculiar dental 

 lamvllte and the vascular impressions. 



Fig. 3. Strophodonta textilis 108 



8 a. A ventral valve of this species. 



8 6. A ventral valve which i» more elongated tlian the usual form. 



8 c. The dorsal side of a large individual, showing the cardinal area of the ventral valve and a 



narrow callosity in the centre. 

 8 d. The interior of a portion of an imperfect dorsal valve, showing the small muscular area and 



slender cardinal process. 

 8 e. An enlargement of the surface, showing the character of striae, etc. 

 4. A cast of a ventral valve which is apparently of the same species, much extended on the 



hinge line. 



