28 



OKEDEN, ON THE DIATOMACEOUS DEPOSITS OF 



Triceratixim comptum ? 

 „ alternans. 



„ armatuni, n. sp. 



Eupodiscus sciilptns. 

 Cam})ylodiscus Hodgsonii. 

 „ cribrosus. 



,, parviilus. 



Surirella ovata. 

 ,, fastuosa. 

 ,, lata. 

 Tryblionella marginata. 

 „ punctata. 



„ acuminata. 



„ scutellum. 



Nitzschia sigma. 

 Amphiprora constricta. 

 Navicula Jennerii. 

 ,, didyma (a). 

 (a')- 

 „ («*). 

 „ punctulata. 

 ,, convexa. 

 ,, elliptica. 

 ,, palpebralis. 



Navicula liber. 

 Pinnularia cyprinus. 

 ,, distans. 



„ peregrina. 



Stauroneis pulchella. 

 Pleurosigma formosum . 

 ,, angulatuni. 



,, Balticum. 



,, tenuissiuiuni. 



Syuedra superba. 

 Doryphora amphiceros. 

 Aclmanthes brevipes. 

 Rhabdonema minutum. 

 „ arcuatum. 



Gram matopliora serpentum . 

 Amphitetras antediluviana. 

 Tstlimia euervis. 

 Biddulphia aurita. 

 „ rhombus. 



,, quinque-oculus, Kutz. 



Podosira maculata. 

 Melosira sulcata. 

 „ Eorreri. 

 Dictyocha speculum. 



I have also two fine specimens of what I thought to be a 

 new Navicula ; but on referring them to Mr. Smith, he in- 

 formed me that it had been already observed by Mr. Hennedy, 

 and it has been named N. Henuedii hy Mr. Smith. It was in 

 this deposit that I found the first specimen of the Triceratium 

 which has been described and named by Mr. Roper as T. 

 armatum. 



The prevailing form, however, is the Namcula Jenuerii, 

 which is extremely abundant. Tlie specimens of Coscino- 

 discus are also magnificent and abundant. 



Of the Triceratia, T.favus, and T. comptum (?) are very 

 abundant. T. alternans occurs but sparingly. 



The beautiful valve of Actinocyclus sedenarius, described 

 by Mr. Roper in his paper on the Thames mud, occurs but 

 sparingly ; all the other forms in the foregoing list are 

 tolerably abundant, and occur also in the 30 and 40 feet 

 deposits. 



T.favus occurs also pretty frequently at both these depths, 

 while in the 30-feet deposit I found a most curious and in- 

 teresting form, of which I have sent specimens. Mr. Smith 

 informs me it is the Cerataulus turgidus of Ehrenberg, and 

 will be the Biddulphia turgida of Mr. Smith's second volume. 

 I am not aware that it has been hitherto figured or described 

 by any one as a British species. 



But it is not always necessary to resort to the boring 

 apparatus to obtain material for investigating these deep 



