[WILLIAMS] FOSSIL FAUNAS OF THE ST. HELEN'S BRECCIAS ^43 



PLATE I. 



Spibifeb Montbealensis. 



A series of the larger sized specimens showing the characters of the mature 

 individuals. 



Figures 8, 4, 1, 5. — Pedicle valves showing the general form, the regular rounded 

 plications on the specimens up to middle growth and the obscuration 

 of the plications toward the front in mature specimens. 



FiGUEE 11. — A specimen showing the angular bottom of the medial sinus of the 

 pedicle valve. 



FiGUBES 2, 3, 9. — Brachial valves, showing the plications and the medial groove 

 in the centre of the medial fold in early stage of growth, and in fig. 2 

 its disappearance from the later stage of growth. 



Figures 7 and 10. — Molds of the exterior of central part of two pedicle valves ; 

 fig. 10 shows the flattening out and obselescence of the plications upon 

 the front portion of the shell in a large specimen. 



Figure 6. — Mold of exterior of a brachial valve showing the angular form of the 

 median fold. 

 All the specimens are from the block of limestone referred to in the paper as 

 252.1 from St. Helen's Island. 



