542 PROF. GREGORY ON NEW FORMS OF MARINE DIATOMACE^. 



form nor in the preceding, have I seen the slightest trace of any tendency to pass 

 into N. Smithii, or into its variety N. fusca. 



I have, indeed, lately noticed one variety of the present form, namely, a pan- 

 duriform variety, agreeing with the type in size, in general aspect, and in the pe- 

 culiar median line. This I shall describe and figure on a future occasion. 



I may here add, that I shall also have to describe and figure another new form 

 of Navicula, occurring abundantly with the preceding ones, which at first I was 

 disposed to refer, like them, to N. Smithii. But I find it so uniformly peculiar, 

 that I must separate it also. 



7. Denticula (?) Icevis, fig. 33. I have some reason to think that I have detected 

 the S.V. of this species. The F.V. is frequent in some densities, but it would 

 appear that the entire frustule is so much broader on the F.V., that it never lies 

 on the S.V., and that the valves are never, or hardly ever, separated. Even when 

 separate, the S.V. must be so very narrow, and perhaps so convex, that this side 

 is not usuallyseen. In one case, however, where one of a group has been partly 

 turned, I think I can see that the S.V. resembles in shape that of D. fulva, only 

 smaller and narrower. 



I have also to add to the list of British species two forms, both remarkable, 

 which occur in Lamlash Bay. 



These are, — 1. Cocconeis Morrisiana, Sm., a very curious species lately found 

 by Professor Smith, I believe, in a gathering from the Levant or from the Black 

 Sea. 2. Pleurosigma compactum, Grev. ; described and figured by Dr Greville, 

 from Trinidad. I propose, in a future paper, to figure these two species as British 

 forms. 



I have just now been able to add to the figures, one of the very remarkable 

 detached segment of Amphora spectabilis, as described in the text. It will be 

 found in PL XIII. , fig. 79 e. 



2%thMay 1857. 



