286 



the valve similar to that in P, stauroneiformis ; but I do not con- 

 sider this enough to constitute a new species. 



Of the mode of occurrence of the Maidstone and Derry depos- 

 its I know nothing, and introduce the lists of the species contained 

 in them here for the purpose of comparison, and in the hope that 

 more will be yet known concerning them. That from Derry con- 

 tains the following species : 



Cocconema cymhiferum. Naviculajirma, 



" parmim, " obiusn, 



Cymbella Ehrenbergii, ' " serians, 



Epithemia gibba, Ortliosira oiichnkea, 



Eunotia/'alx, Pinnularia nobllis, 



" ietraodon, " viridis, 



Gomphonema acuminatum^ Slaiironeis gracilis^ 



" citspidatuni, Tabtllaria ftnestrata. 

 Himaniidium gracile, 



Navicula ohtusa (misprinted ohtusata in Smith's Synopsis) has 

 not hitherto been found in this country ; neither has Eunotia 

 falx ; and I believe this is, as yet, the only locality here for either 

 of them. 



The 3Iaidstone deposit contains the following species : 



There are also one or two species of Himantidiwn found in 

 this deposit, but, as this branch of botany is at present in a very 

 confused state, and I do not find them described in any reliable 

 work on the subject, I refrain from giving them names. The 

 habit of describing species from deposits is one that cannot be too 

 strongly deprecated, tending as it does to crowd our Botanies with 

 synonyms, not only useless, but really hurtful to the science. No 

 new species can be correctly described from the dead plant alone. 



The Hirigham deposit was found on the estate of Mr. T. T. 

 Bouve, in an orchard, supposed to have been formerly a pond. 

 It is six or eight inches in thickness, covered with a vegetable 

 mould and earth, apparently washed down from surrounding high 

 ground, of a foot or so in depth. There is, however, no peat 

 present, all of that substance originally present having been 

 changed into this white earth. This deposit was at first taken 



