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1463 



TERTIARY FAUNA OF FLORIDA h 



The earliest American species is Cretaceous, but very little attention has 

 been paid to the group in our Tertiary, though they exist in nearly all the 

 freshwater Tertiaries of the west. 



The group may be arranged as follows : 



Genus Corneocyclas Ferussac. 



Subgenus Corneocyclas. Type Tellina pusilla Gmelin. 



Nepionic shell convex, concentrically striated; hinge with two separate 

 cardinals in the left, and a single compound, usually arcuate, cardinal in the 

 right valve. 



Section Corneocyclas s. s. Type Tellina pusilla Gmelin. Hamburg, 



Germany, type locality. 



Nepionic valves passing into the mature disk without any strong demarca- 

 tion; the anterior cardinal and lateral adjacent and retaining traces of their 

 original connection; ligament internal. 



Section Phymesoda Rafinesque. Type Tellina virginica Gmelin. Vir- 

 ginia. 



Like Corneocyclas s. s., but the anterior laterals distant and unconnected 

 with their respective cardinals ; the ligament partly external. 



Section Pisidium C. Pfeiffer. Type Tellina amnica Miiller, 1774. 



Denmark. 



The two right cardinals not consolidated, the larger cardinal in each valve 

 bifid, the smaller one slender, entire ; the laterals distant ; the ligament internal. 



Section Cy do calyx Ball. Type Pisidium Scholtzii Clessin. Breslau, 



Germany. 



Valves subconstricted near the junction of the nepionic shell with the disk, 

 the umbones high and calyculate, otherwise like Corneocyclas s. s. 

 Subgenus Cymatocyclas Dall. Type Pisidium compressum Prime, 1851. 



Fresh Pond, Cambridge, Massachusetts. 



Nepionic valves flat, transversely undulated, sharply delimited from the 

 curved surface of the disk ; hinge-teeth as in Corneocyclas, the cardinals feebly 

 developed ; ligament internal. 

 Subgenus Tropidocyclas Dall. Type Pisidium Henslowianum Sheppard. 



County Suffolk, England. 



Nepionic valves with an oblique, elevated radial keel, and distinctly de- 

 limited from the curved portion of the disk; cardinals as in Corneocyclas; 



