MEMBHANIPORA PILOSA. 139 



and occupies almost the whole of the front of the cell j more 

 commonly it is placed at the upper part of it, occupying 

 about half its length or less. In the former case an 

 approach is made to the form which we have in M, mem- 

 branacea, in which the prolongation of the cell below the 

 aperture is almost entirely wanting. 



Besides these variations in the structural details there 

 are others in the habit of growth (Vars. /3 and 7). 



Habitat. On stones and shells (var. dentata) from the 

 Coralline ground and from deep water, and on Laminaria 

 and other Algse (masses of which are often completely 

 coated by it), Sertularians, &c., between tide-marks and 

 in shallow water. 



Locality. Universally distributed on our coasts, and 

 extremely abundant. 



Geographical Distribution. Roscoff, everywhere 

 abundant on Fucus serratus, and especially on Rhoily- 

 menia paJmata (Joliet) : Belgium (Van. Ben.) : Mediter- 

 ranean (Risso) : Adriatic, common (Heller) : Aden ; Ara- 

 bian Sea, on weed taken up between Bombay and Aden, 

 lat. about 15° N., long, about 65° E. (W. Gates) : Mel- 

 bourne; New Zealand (T. H.): Norway, var. laxa (Sars) : 

 Hougesund ; Heligoland, about 100 fms. (Kirchenpauer) : 

 Finmarck (Goes and Malmgren) : Greenland (Liitken) : 

 Gulf of St. Lawrence ; Nova Scotia (Dr. Dawson) : South 

 Labrador, common on Desmarestia, just below low- water 

 mark (Packard) : var. stellata, New Jersey and Rhode 

 Island, on Lam. saccharina, &c., common (Leidy) : Baltic, 

 Eastern basin, abundant (K. Mobius). 



In its more delicate forms, as developed in the hollow 

 of a shell, or spreading, as I have seen it, over the surface 

 of one of the red Algse, this is a beautiful species. Its 

 little cells have a metallic lustre, and almost look as if 



