456 Mr. C. Grave on the 



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. 



LXI. — Embryology of Ophiocoma echinata, Agassiz. 

 (Preliminary Note.) By C. Grave*. 



The conflicting results of previous investigators, and the need 

 of confirmation of some of the results obtained by them upon 

 Ophiurid development, seemed to warrant my undertaking a 

 new investigation of the subject; and by the advice of 

 Prof. W. K. Brooks it was made my principal object while 

 in Jamaica during the summer of 1897 to obtain a series of 

 embryological material extending at least from the segmen- 

 tation stages to the beginning of metamorphosis. 



But when I arrived at Port Antonio on June 14th I found 

 that in no species at hand had the breeding-season begun 

 except with Ophiocoma Riisei, with which it was over, and 

 it was not until less than three weeks of the end of my stay 

 that the first ripe eggs were thrown by Ophiocoma echinata, 

 although ripe spermatozoa had been obtained every day for 

 more than a month. 



In consequence of this the oldest plutei reared were but 



* From the ' Johns Hopkins University Circulars,' November 1808, 

 pp. 6-7. 



