68 COMMON SEAWEEDS. 



in form, thin as paper, very brittle, fastened by the 

 middle of each frond, and the edges are free, yet the 

 masses are dense, for the fronds overlie each other, 

 and are spotted with ceramidia, or urn-shaped cells, 

 containing each four spores or tetraspores. When a 

 portion of this Melobesia is soaked in weak muriatic 

 acid, the coating of lime is removed, and a most deli- 

 cate zoned structure is revealed by the microscope. A 

 few minutes will remove the deposit of lime. Wash 

 the portions in a watch-glass, and, with a camel-hair 

 pencil, place a morsel on a glass slide, with a drop of 

 water, cover it with a thin piece of glass, and observe 

 how this apparent stone is really a beautiful vegetable 

 structure. 



On Zostera, Phyttophora, and Clwndrus Crispus we 

 find varieties of Melobesia worth examining. 



CATAKELLA OPUNTIA 



(Name meaning a " little chain.") 



This may be found even at high-water mark on 

 the woodwork of breakwaters, or in crevices of large 

 boulders. Colour, a very dark purple, almost black 

 when dry, and not adhering well to paper. The 

 creeping fibres at the base of the frond are densely 

 matted, and chain-like cells rise about an inch high. 



Fructification. — Two kinds worthy of attention. 1. 

 A berry, usually in the place of an abortive ramu'li or 

 branchlet, in which is a mass of spores, called favellce. 

 2. Tetraspores, transversely parted, and surrounded 



