14 Mr. F. Walker's Descriptions of Aphides. 



scattered in the various works on natural history, may have 

 escaped my attention. 



All malacologists are acquainted with the existence of the hya- 

 line cylindrical elastic stylet that is found in the bodies of all 

 bivalves, whether great or small ; I have seen this organ men- 

 tioned in a work on natural history that has escaped my memory, 

 with the addition that its use is entirely unknown. Whilst dis- 

 secting the Pholadidea papyracea and other Pholades, in which 

 this stylet is easily detected, and in which the larger end is im- 

 bedded in the muscular fundus of the body and foot, instead of 

 drawing it forth as I had often done, I was induced to trace its 

 course, and found that it terminated in the stomach, and had 

 attached to it a light yellow doubled-up corneous subtriangular 

 plate, wrinkled into three bluntly pointed lobes at one end, and 

 at the other a membrane by which it is affixed to the elastic 

 stylet. This discovery at once made evident the use of this ap- 

 pendage, and that it was an elastic spring to work the corneous 

 plate or attritor, by the muscular action of the foot and body, to 

 divide and comminute the food, and especially the minute crus- 

 taceous and testaceous alimentary matters received into the sto- 

 machal cavity ; it appears then that this appendage acts as a giz- 

 zard, and the Bivalve Mollusca are thus supplied with a mastica- 

 tory apparatus very analogous to the gizzards of some of the 

 Gasteropoda. 



I am, Gentlemen, your most obedient servant, 



William Clark. 



III. — Descriptions of Aphides. By Francis Walker, F.L.S. 



[Continued from vol. iv. p. 202.] 



72. Aphis Persica, Sulzer, &c. 



Aphis Persica has been described by several authors, but T 

 believe that this name will apply to two species, and I defer 

 giving the references until I can ascertain to which of these they 

 most probably belong. 



This Aphis feeds on the peach, Amygdalus Persica, in Europe 

 and in North America, and on the sloe (Prunus spinosa) ; the 

 latter tree is its original habitation, but the introduction of the 

 peach into England caused a partial change in its nourishment. 

 It sometimes passes from the peach to the cherry, and multi- 

 plies thereon. Schmidberger states that there are sixteen gene- 

 rations in one year, and that some of the young ones of the 

 second generation acquire wings. 



The viviparous wingless female. It appears on the buds of the 

 peach-tree before the end of March, and when young is very 



