EXPLANATION OF PLATES. 173 



Fio. 2.— OSTEEO YELENUNA. 

 Fig. 2 a, h. Exterior and interior of upper valve. 



PLATE XVIII. 



Fig. 1.— OSTREA CONTRACTA. 

 Fig. 1 a. Exterior view of a narrow valve. 



1 b. Exterior view of a shell of the usual form. 



1 c. Interior and lateral view of larger valve. (Figures one-third, in linear measure- 

 ment, of the originals.) 



1 d. Enlargement of surface of the ligamental pit. 



PLATE XIX. 



Fio. 1.— ANOMIA SUBCOSTATA. 

 Fig. 1 a, h. Exterior and interior of lower valve. 



Fio. 2.— CAEDITA PLANICOSTA. 

 Fig. 2 a. Left valve, natural size. 



2 h. Enlargement of surface, showing concentric 8tria3. 



Fio. 3.— PHOLADOMTA TEXANA. 

 Fio. 4.— COKBULA NASUTA. 



Fio. 5.— VENUS VESPERTINA. 

 Fig. 5 a. Eight valve, natural size. 

 5 b. Enlargement of surface. 



Fio. 6.— VOLUTALITHES SAYANA. 

 Fig. 7.— NATICA EJIINCLA. 



Fig. 8.— TUEKITELLA ? 



Fio. 9.— CASSIDULA (LACINLV) ALVEATA. 



Fig. 9 a. View of the aperture. 

 9 b. Back of the shell. 



PLATE XX. 



Fig. 1.— COLUMNAKIA THOML 



Fig. 1 o. A fragment of stone with the coral, (ends of columns,) natural size. 

 1 b. Lateral view of same. 

 1 c. Longitudinal section enlarged. 

 1 d. Transverse section enlarged. 



Fio. 2.— TEREBRATULA MEXICANA. 

 Fig. 2 a, b, c. Dorsal, ventral and profile views. 



