PLATE Xi. 
5. Productus umbonillatus, Avmg. Cast (natural size) of the convex valve, showing 
impressions of the superior pedicle muscles (a), and of 
the valvular and cardinal ditto (6) conjoined. Tunstall 
18. 
19 
20 
Hill. 
(The letter a points too much to the left.) 
— — Small valve of the last specimen. 
— as Gutta-percha cast of the flat valve of the same, showing 
the boss or cardinal muscular fulerum (a); median 
plate (4); reniform impressions (/); impression of a 
vein connecting the latter structures with the medio- 
cardinal region (¢). 
(The dotted line connecting the letter a with the boss has been 
inadvertently omitted.) 
— — Medio-longitudinal section: a, large valve; 4, small valve. 
The inferior side of the prolongation (umbone) on the 
right side of the figure represents the flattened (or 
area-like) space on that side of the umbone adjoming 
the hinge. 
. Strophalosia Goldfussi, dznster. Ideal medio-longitudinal section: a, area of 
large valve; 4, ditto of small valve. 
. Strophalosia excavata, Geznitz. 
. Strophalosia Morrisiana, King. 
Ideal medio-longitudinal section. 
Ideal medio-longitudinal section. 
