TRANSACTIONS OF WAGNER 



I2 3 8 



TERTIARY FAUNA OF FLORIDA 



or normal adult specimens. After passing the groups where the hinge is more 

 or less rugose or peculiar and reaching the most typical forms of the subfamily, 

 such as Meretrix, we may observe two types of hinge which in peripheral 

 species, as in their evolution in time, tend towards each other. 



A. Meretrices in which the development of the teeth is checked, while the 

 primitive laminae still connect what would normally be distinct cardinal teeth, 

 as in the left valve the two anterior cardinals, in the right valve the anterior 

 and posterior cardinals, so that when the valves are closed the arch of the left 

 valve spans the right middle cardinal and the arch of the right valve spans that 

 of the left, separating it from the dorsal hinge-margin, while the left posterior 

 cardinal and the anterior laterals are left isolated. The formula is L - 



R. oioioi.ioi 



There may also be a groove in the left anterior and right posterior dorsal 

 margin to receive the bevelled edge of the opposite valve, but this is not 

 invariable. 



B. Meretrices in which the development of the cardinals continues until 

 the right ones are separated from each other, and, in the adult shell, appear to 

 start from a point on the dorsal margin immediately below the umbo. The 

 formula will then be the same as in the preceding division with the omission 

 of the connecting brackets. Traces of the original connection sometimes remain 

 visible (Amiantis), but the teeth are in touch with the dorsal margin, from 

 which in Callocardia and Agriopoma they are separated by a deep groove. 



Genus G-RATELOTJPIA Desmoulins 

 Donax (sp.) Basterot, Geol. env. Bordeaux, p. 84, 1825. 

 Grateloupia Des Moulins, Bull. Soc. Lin. de Bordeaux, ii., p. 243, 1828; Donax irregu- 



laris Basterot; Deshayes, Encyc. Meth., iii., p. 173, 1830; Bronn, Leth. Geogn., p. 



956, 1838; Ind. Paleont, i., p. 552, 1848; Sowerby, Conch. Man., ed. ii., p. 155, 1842; 



Hoernes, Fos. Moll. Wiener beck., ii., p. 148, 1870; Fischer, Man. de Conchyl., p. 



1081, 1887. 

 Gratelupia Rang, Man., p. 307, 1829; Lea, Contr. Geol., p. 59, 1833; Potiez et Michaux, 



Gal. de Douai, ii., p. 419, 1844. 

 Cytheriopsis Conrad, Am. Journ. Conch., i., p. 146, 1865 (Cytherca hydana Conr.), iii., 



p. 14, 1867; Stoliczka, Cret. Pel. India, p. 154, 1871; not Cytheropsis McCoy, 1849, 



Crustacea. 



This genus appears to be the precursor of Tivela, in which the rugosities of 

 the hinge have not become all fully developed into separate cardinal teeth. It 



