MEMORANDA. 155 
Pleurosigma angulatum, P. macrum, Nitzschia sigmoidea, 
Grammatophora subtilissima, and Surirella gemma. 
One must not believe, then, that, in order to attain such a 
result, it is necessary to make use of the large heliostal 
of M. Foucault, constructed by Dubose, of Paris, or by any 
other optician, and which is alluded to by Count Castracane 
in his letter to R. P. Secchi. A simple cone in flint, such 
as Amici indicated, is far from sufficient for observing micro- 
scopical phenomena. Nevertheless, the heliostal of M. Fou- 
cault may be used advantageously in order to obtain good 
photographic proofs. 
The mode of illumination we are occupied with is not, in- 
deed, sufficiently known; yet M. Nachet had touched the 
matter in the number of July, 1860, of your Journal (p. 208) 
in reference to his dark-ground illuminator. 
Besides, the use of monochromatic light has been recently 
advised in a very good work—‘ La Photographie appliquée 
aux Recherches Microscopiques,’ Bailliére, Paris, 1866. But, 
as it is easily seen by the title itself, the question is more 
especially respecting photographic proofs than to microscopic 
researches. Notwithstanding, I invite all micrographers not 
to neglect this mighty mode of investigation. 
Please to accept, gentlemen, the assurance of my best re- 
gards—MovcueEt, Rochefort-sur-Mer. 
XX 
P.S.—Peu habitué a écrire en anglais, je vous prie d’ex- 
cuser mes incorrections, et de les corriger, si vous voulez bien 
insérer cette note dans le prochain numéro de votre journal. 
Je pourrai, parfois, vous adresser quelques articles concernant 
la micrographie. 
New Curious Animalcule.—Seeing you have reported in your 
Journal No. XX, New Series, the very strange form of 
Lang’s Difflugia triangulata?, I thought it would perhaps 
interest your readers to have a hint of a new, not less rare 
case of these proteform beings, which I have just met with, 
examining some water I have lately taken from a rivulet 
streaming out from the Gower Peninsula between Swansea 
and Oystermouth. The odd fellow I am speaking of was 
protruding itself from its tiny shell, not in the ordinary 
radical way, as its original name of rhizopod purports, but in 
a perfect symmetry with its oval carapace, as to look at first 
like two equal difflugiz in conjunction, and what was more 
astonishing still to me was a hinder expansion of the cara- 
pace in the shape of a tail, for what purpose I really could 
