The Diatoms of the London Clay. By F. Kitton. 387 



ments of Coscinodisci more or less transparent, but tliey disappear 

 when acidized. 



The diatoms in the London clay are probably contemporaneous 

 with those found by Ehrenberg in marl from ^gina, and are there- 

 fore the oldest fossil remains of these organisms. (Their occurrence 

 in the chalk, as stated by Ehrenberg, is undoubtedly erroneous. 

 The few forms figured by him are from fresh water, and probably 

 quite recent.*) 



The following list comprises all the forms hitherto detected in 

 London clay : — 



Arachnoidiscus Ehrenhergii (??) .. .. Very rare. 



Actinoptychus (Actinopha^iia) splcndens One valve only. 



Coscinodiscus perforatus (?) Common. 



„ radiatus (?) Frequent. 



„ rohustns (?) Rare. 



,, suhtilis (?) ,, 



„ minor (?) Frequent. 



Craspedodiscus (?) One valve only. 



Ffjxidicula Hare. 



I Small fam., com- 

 mon in the Prit- 

 tlewell gathering. 



Triceratium alternans One valve only. 



„ favus ,, ,, - 



„ acutum (?). 



Solium exsculptum Eare. 



Corinna elegans (?) ,, 



Hemiaulus hostilis (?) .. „ 



Eupodiscus Argus {? ?) „ 



Synedra (? ?). 



Forms found by Dr. Bossey (those with * named by Mr. Kitton from sketches by 



Dr. Bossey). 



Triceratium (4 species). 



* „ duhiuin. 

 Trinacria regina. 



* Coscinodiscus symmetricus. 

 Corinna elegans. 



*Pyocilla sp. (?). 

 Hemiaulus poly cy stinorum. 



*Xanthiopyxis sp. (?). 



Arachnoidiscus. 



Craspedodiscus (??). 

 * Stictodiscus (?). 

 *Biddulpliia elegantula (?). 



* Terpsinoe on BiddulpMa. 



By Dr. Stolterfoth, M.A., &c., Chester. 



Trinacria excavata. Hemiaidus (cmtarcticus). Eupodiscus Argus. 



By Mr. G. D. Brown, Ealing. 



BiddulpMa aurita. Synedra (?) on Nitzschia (?). Triceratium (?) sp. (?). 



By Mr. Shrubsole. 

 LiostepJmnia rotula (one specimen only) and most of the above species. 



* Although there is no satisfactory evidence of diatoms ever having been found 

 in the chalk, their existence in the Cretaceous period is extremely probable. And 

 if Mr. SoUas' suggestion (Eep. Brit. Assoc , 1879, p. 350), that the silica of certain 

 siliceous sponges has been replaced by lime is correct, we have a clue to the 

 absence of diatoms in the chalk, the carbonate of lime having in like manner 

 replaced the silica of the diatom valve. 



