380 Correspondence — Mr. W. Davies — Prof. Bonney. 

 coI^I^ESI=OI^IDJBI^^CE. 



NOTES ON CHELONIA. 



Sir, — In the interesting " Notes on Chelonia from the Purbeck, 

 Wealden, and London-clay," by Messrs. Lydekker and Boulenger, 

 in the May Number of this Magazine, the authors refer to the generic 

 identity of the plastron named by Prof. Sir E. Owen Platemys 

 Bullockii, supposed to have been obtained from the London-clay at 

 Sheppey, and the plastra of the same author's genus Pleurosternon 

 from the Purbecks. In regard to which will you allow me to state, 

 that when arranging the fossil Chelonia, some fourteen or fifteen 

 years ago, in the Museum cases at Bloomsbury, I observed that the 

 structural characters of the plastra of Platemys BullocTcii and of 

 Pleurosternon were the same, and that the two genera must be merged 

 into one. This conclusion was further confirmed by a closer exami- 

 nation of the matrix adherent to the former, which proved it to have 

 been derived from the Purbecks, and not as stated from the London 

 clay. The specimen has ever since been exhibited in the Museum 

 cases with the following label attached, " Pleurosternon (Platemys) 

 Bullockii, Owen, Purbeck beds, Swanage." 



Though the locality is not positively known, there can be little 

 doubt that the specimen was found in the " Isle " of Purbeck, and in 

 the neighbourhood of Swanage. Prof. Eiitimeyer's remarks upon 

 the same subject were, I am sorry to admit, unknown to me until 

 very recently. Wm. Davibs. 



THE LIZAED SERPENTINES. 

 Sir, — It appeared to me that, in regard to the existence of felspar 

 in the Eill serpentine,' lately in dispute between Mr. Teall and 

 myself, the evidence of a chemical analysis of the rock would do 

 much to clear up the question. Through the kindness of Dr. S. 

 Eideal, a partial analysis of this serpentine has been made in the 

 Chemical Laboratory at University College with the following 

 results in two cases : — 



86-89 87-13 



The water, alkalies, etc., were not estimated, as I had said that 

 probably the silica, alumina, and magnesia would suffice for my 

 purpose. At first sight this analysis appears conclusive in favour of 

 Mr, Teall's contention, that there is felspar in the rock. It is the 

 analysis of a picrite, so far as such a variable rock can be said to 

 have a typical analysis. Indeed, the proportion of alumina is large 

 even for a picrite. But I still feel perplexed, for on consideration 

 of the analysis it appears to me to " prove too much." Suppose the 

 alumina all present in the felspar, and that to be anorthite ; for 

 1 See Geol. Mag. Feb. 1887, p. 69, and March, 1887, p. 137. 



