TRANSACTIONS OF WAGNER 



TERTIARY FAUNA OF FLORIDA 



gigantea of Gmelin (=nimbosa Solander), but this is only sectionally distinct 

 from the forms which have been called Dione and Callista, and Meek's name 

 will therefore have to be taken as covering them both, while a new sectional 

 name is adopted, which was proposed by Cossmann for Eocene members of 

 the group named Dione by Gray in 1838. 



The characteristics of the genus are as follows : 



Shell ovate, solid, porcellanous, microscopically radially lineated, polished, 

 smooth or concentrically waved, usually with a vivid coloration and vernicose 

 periostracum ; lunule definitely limited, unequally divided, the right portion 

 slightly larger, internal margins smooth ; pallial sinus ample, pointed in front ; 

 left anterior and right posterior dorsal margins grooved to receive the edge of 

 the other valve ; the anterior laterals and three cardinal teeth present in each 

 valve, the right posterior cardinal more or less distinctly grooved or bifid. 



Section Macrocallista s. s. 



Shell elongated, the pallial sinus short, the nymphs smooth, the posterior 

 cardinals very slender and elongated. Type Venus nimbosa Solander. Florida. 



Section Chionella Cossmann, 1886. 



Shell ovate-trigonal, the posterior cardinals short, the pallial sinus reaching 

 to the middle of the shell, or nearly. Type Cytherea ovalina Lamarck. Parisian 

 Eocene. 



In the recent species, like Venus chione, the sinus is nearly horizontal, its 

 apex pointing below the anterior adductor scar ; in the Eocene species it is 

 more elevated, and in C. ovalina, which Fischer selected as type (Cossmann 

 having mentioned no type), it points to the upper margin of the anterior scar. 

 But this distinction seems insufficient to base any further subdivision upon. In 

 a general way this section differs from Macrocallista proper in being shorter 

 and more trigonal, the other characters mentioned being functions of the differ- 

 ence in form. 



. Macrocallista reposta Conrad. 



Cytherea reposta Conrad, Journ. Acad. Nat. Sci. Phila., vii., p. 132, 1834; Fos. Medial 



Tert., p. 15, pi. ix., fig. 2, 1838. 



TCytherea pandata Conrad, Journ. Acad. Nat. Sci. Phila., vii., p. 132, 1834 (young shell). 

 Cytherea reporta Emmons, Geol. Rep. N. Car., p. 294, fig. 2230, 1858; not C. reposta 



Emmons, loc. cit., fig. 222 (= C. albaria Say). 

 Dione reposta Conrad, Proc. Acad. Nat. Sci. Phila. for 1862, p. 575, 1863 ; Meek, Checkl. 



Miocene Fos., p. 10, 1864. 



