1845.] Linnean Society. 233 



arranged the ordinary coniferous dots, to the outside of which (pro- 

 jecting beyond the outUne of the fibre when seen obliquely) adhered 

 small bodies of the same size which bore the precise representation 

 of the coniferous disc, and were evidently casts of cavities existing 

 in the original plant : some of these were also seen detached. These 

 appearances, Mr. Quekett states, prove the correctness of the mo- 

 dern belief, that the discs are formed by depressions on the outside 

 of the walls of two contiguous fibres, giving rise to cavities of a len- 

 ticular form. 



Mr. Quekett concludes his paper with some observations on the 

 process of silicification in its various stages and modifications ; and 

 endeavours thereby to account for the readiness with which some 

 silicified woods break down into separate portions, exhibiting perfect 

 casts of the organs within which the siliceous matter was deposited, 

 while others are cemented into a mass incapable of organic sepa- 

 ration. 



Read also " Notes on the Variations of Structure in the British spe- 

 cies oi Eurytomid(B." By Francis Walker, Esq., F.L.S. &c. 



In this paper Mr. Walker enumerates the variations in each seg- 

 ment of the British Eurytumidce, and comes to the conclusion that, 

 in grouping the species of a genus of this family, the primary divi- 

 sions may be formed from the variations of the thorax, and the secon- 

 dary divisions from the variations of the abdomen, of the antennae, 

 and of the nervures of the wings. He regards Eurytoma as the ty- 

 pical genus of the family ; and believes that the three genera Isosoma, 

 Systole and Decatoma converge towards it by as many radii. An un- 

 described genus, to which Mr. Walker gives the name of Porcia, is 

 nearly allied to Decatoma, and is thereby connected wich Eurytoma. 



Mr. Walker takes a summary view of the three genera Eurytoma, 

 Isosoma and Decatoma, noticing under each the peculiar characters 

 of the genus and the modifications to which they are subject. He 

 points out the number of variations which occur in the British spe- 

 cies in the structure of their segments, and gives arranged lists of 

 the species, commencing with those which are most characteristic of 

 the genus, and ending with those which are least so. 



Read also the conclusion of Mr. Doubleday's " Remarks on the 

 genus Argynnis of the ' Encyclopedic Methodique,' especially in re- 

 gard to its subdivision by means of characters drawn from the neu- 

 ration of the wings." 



Mr. Doubleday commences by referring to the successive attempts 



