258 ADDENDA. 



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

 gilis of Montagues plate 5, lig. 1, which seems to be of this genus. 



Agina purpurea, p. 54. 

 In Mrs. Griffiths'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 pygmseus, 

 which partially clothes the rocks at half Hood. 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 destruc- 

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

 within our knowledge, of a marine bivalve being strictly vivi- 

 parous, or producing the fry In a perfectly formed state. Its 

 animal structure and functions must consequently be analagous 

 to the fresh water bivalves. This may account for the vast num- 

 bers collected tosrether. 



'» 



Mactka crassa, p. 69. 

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

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

 solida. 



Mactra glauca, p. 73. 

 We have some fine specimens of this shell, dredged in Corn- 

 wall. 



Psammobia Scopula, p. 98. 

 In the summer of J 820, great numbers of this species and the 



