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TERTIARY FAUNA OF FLORIDA 



dip obliquely into the valves. In one case observed the ends of the ligament 

 descended one in front and the other behind the upper end of the resilium, but 

 the normal position is in front of the resilium. The lunule and escutcheon 

 when present are compressed and almost linear, the dorsal margin of the flat 

 valve usually slightly overlies that of the convex valve. The pallial line is in 

 this genus largely a misnomer, for the mantle is attached to the shell by a 

 succession of rounded spots which are not continuous ; the visceral area of the 

 disk may be smooth, but is often punctate or radially striate and brilliantly 

 pearly. The left valve is the convex one, and the ventral margin of the right 

 valve is generally more or less flexible, so that there is an entering angle above 

 it when the shell is closed so that the solid portions of the valves come to- 

 gether. The pearly layer is overlaid by a conspicuous, often partly eroded, 

 prismatic layer, and that by a periostracum which in the northern species is 

 often rather profuse and papery. The margin is practically entire, but they 

 often have a few radiating threads on the posterior slope of the left valve, while 

 on the right valve, especially in Kennerleyia, there are usually radial, impressed, 

 somewhat dendritic brown lines. 



The species are usually found in sandy or muddy situations, and the group 

 is represented as early as the Cretaceous in Europe. 



The group may be divided as follows : 



Subgenus Pandora s. s. Type P. inaquivalvis Linne. 



Two cardinals in the right valve ; one obscure cardinal or none in the left 

 valve ; no lithodesma ; sculpture of the right valve feebly concentric. , 



Subgenus Kennerleyia Cpr. (em.). Type K. filo$a Cpr. 



Like Pandora s. s., but provided with a lithodesma ; the right valve radially 

 sculptured. 



This was named after Dr. Kennerley, and the corrected spelling proposed 

 by Fischer is better than that used by Carpenter. 



Subgenus Ccelodon Carpenter. Type Pandora ceylanica Sowerby. 



Left valve with a normal posterior and an anterior A-shaped cardinal ; right 

 valve with three distinct subequal cardinals but no lithodesma. 



Subgenus Clidiophora Carpenter. Type C. claviculata Carpenter. 



Left valve with three laminae, two in front and one behind the resilium, the 

 anterior ending behind the anterior adductor scar, the posterior much elongated ; 

 right valve with a very long posterior lamina, an elevated pedunculate median 



