258 



should be called Listera fragilis, with reference to the Mactra fra- 

 gilis of Montagu's plate 5, fig. 1, which seems to be of this genus. 



Agina purpurea, p. 54. 

 In Mrs. GrifRths's cabinet we remarked a specimen exactly like 

 our figure, of a purple color, dredged in Torbay. 



Kellia rubra, p. 57. 

 Found in prodigious numbers imbedded in the Fucus pygmaeus, 

 which jmrtially clothes the rocks at half flood. In the month of 

 June, the greater part of them are filled with perfectly formed 

 young ones, about twelve in number, flat and of a pale red color, 

 and completely filling up the cavity of the valves, to the destruction 

 of the parent, like the Cyclas cornea. It is the only instance, within 

 our knowledge, of a marine bivalve being strictly viviparous, or 

 producing the fry in a perfectly formed state. Its animal struc- 

 ture and functions must consequently be analagous to the fresh 

 water bivalves. This may account for the vast numbers collected 

 together. 



Mactra crassa, p. 69. 

 Not uncommon at very low tides at the entrance of the rivers 

 Dart and Teign: certainly a very distinct species from the Mactra 

 solida. 



Mactra glauca, p. 73. 

 We have some fine specimens of this shell, dredged in Cornwall. 



PsAMMOBiA Scopula, p, 98. 

 In the summer of 1820, great numbers of this species and the 



