Mr. T. Scott on Cytheridea castanea. 456 
species recorded by Prof. Jones include several Ostracoda, 
but none of them appear to belong to the Cytheridea referred 
to here. Moreover, the shell-bed in which this Ostracod 
occurs is apparently referable to a later date than the deposit 
in which the Bahia fossils were obtained that are described 
by Prof. Jones. 
The <Azara is said to be still living in the estuary of the 
Plata, and probably the Cytheridea may also be still living 
there; for if the same conditions that were suitable to the 
existence of the Azara when the bed in which they are now 
found fossil was being: formed were also congenial to the 
Cytheridea, it is reasonable to suppose that the conditions 
under which the mollusk is living now will also be favourable 
to the existence of the Ostracod. 
The figures on the annexed Plate XVI. represent (1) a 
sketch (fig. 1), drawn from memory by Mr. John Scott, of 
two of the dunes, to indicate approximately the position of the 
shell-beds in which the fossils occur, and (2) two drawings 
(figs. 2 and 3) by Mr. A. Scott, showing a lateral and a 
dorsal view of the Ostracod, prepared from Buenos Ayres 
specimens. 
