206 PROCEEDINGS OF SOCIETIES. 
have wished, that is to say, a day or two after casting its shell—he, 
however, took the thinnest he could find. He examined the thinnest 
part of it, near the edge, and was able to perceive that the first 
deposit consists of crystals of carbonate of lime of beautiful stellate 
and aigrette forms, not aggregated in masses, but scattered thinly 
over the skin with distinct naked patches between. On examining 
the sides and upwards towards the dorsal part of the shell he 
found the erystals packed more and more closely together, until 
finally the crystalline structure became indistinguishable, and, so 
far as he could make out, the interspaces being formed with amor- 
phous granular particles like powdered chalk; indeed, he was not 
sure that the whole mass of crystals may. not be finally transformed 
into something of that sort. All the crystals found were of such 
forms as he believed were found only in animal secretions, it there- 
fore occurred to him that the first layer of crystals is secreted by 
the creature, and this layer forms a basis of attraction for the 
remaining portion, which is probably segregated from the water in 
the same manner as incrustations are formed on many substances 
immersed in water holding lime in solution, whilst on other sub- 
stances immersed in the same water no deposit is formed. 
Vacuolaria virescens, Cienk., shown.—Mr. Archer showed an en- 
cysted state of the flagellate Vacuolaria virescens, Cienkowski. 
Before making a note of it here, however, he desired to refind some 
examples ; this organism is somewhat local in its occurrence, but 
in its own situations sometimes occurs in considerable quantity. 
Bacterium rubescens, Lankester, exhibited on part of Mr. Lan- 
kester.—Mr. Archer showed examples kindly given to him by Mr. 
Ray Lankester of his remarkable Bacterium rubescens. Mr. Archer 
at same time drew attention to Mr. Lankester’s figures accom- 
panying his valuable memoir thereon, as well as to some related 
forms of undoubted algal nature opportunely turning up. When 
Mr. Lankester showed this organism to him, on the occasion of 
the meeting of the British Association at Belfast, he was under 
the impression it might turn out to be identical with some one of 
the things now on the table, only in much more exuberant condition 
of growth, having an affinity to that named Clathrocystis aeruginosa 
by Henfrey, or that named Monostroma rosea by Currey; but 
though no doubt ‘related,’ and probably an alga, Mr. Archer 
thought he could most safely say Mr. Lankester’s B. rubescens 
was not identical with any of them. 
Staurogenia rectangularis (Morren), A. Braun, exhibited.—Mr. 
Archer showed the rather uncommon minute alga Staurogenia 
rectangularis, A. Braun=Crucigenia rectangularis, Morren= Chlo- 
ropedium rectangulare, Nig. On the appearance of Mr. Archer’s 
paper in reference to the genus Tttrapedia, Reinsch, in the 
‘Quart. Journ. Micr. Science, M. Morren, fil., was under the 
impression that Zetrapedia was but a new name for the same or 
one very similar to the organism discovered by his father, but it is 
not so. They are essentially distinct things—the present plant is 
chlorophyllaceous, Tetrapedia phycochromaceous. 
