132 



encrusting stones and forming its cells like a Flastra, in large 

 circumscribed patches. The first appearance of its rising 

 into a lamellated form, is the production of detached ridges 

 and papillary eminences, as these become more elevated they 

 assume the form described above. 



The growth of the cells appear to be periodic and rapid ; 

 formed, in the first place very delicately, and afterwards 

 completed and strengthened by depositions of calcareous 

 matter. In almost every specimen, bands of this periodic 

 growth are to be seen varying from half-an-inch to one inch 

 in depth. If these bands be carefully examined it will be 

 found, that all the cells composing them are nearly in the 

 same condition of growth ; each band differing from the 

 other. Hence the poSypidom is frequently marked by ridges, 

 which indicate the extent of the various enlargements; and 

 the whole process of the growth of the cells, from the mere 

 gelatinous e {fusion, to the complete obliteration, can be ob- 

 served in a single specimen. 



The form of the cells varies with the form of the poly- 

 pidom, yet every change can be considered but as variations 

 of one form from mechanical causes. When the extension 

 takes place in the encrusting form, the effusion of the pulp is 

 more extensive than in the erect and foliaceous state. In 

 this, lime is rapidly deposited and the cells appear larger and 

 not so much crowded as in the other kind, so that the growth 

 is effected here as it is in Lcpralia, F/ustra, &c. The cells, 

 which are superficial and on both sides of the leaf when 

 erect, stand on a solid base which unites both surfaces. 

 They present three varieties of appearance the first of which 

 is the semi-gelatinous or pulpy state, the second wliere the 

 surface is granular, from the fully developed cells, and the 

 third is the confused appearance produced by the partial 

 and complete obliteration of the ceils, 



ALC YONIB t T L M* 



Polypidoms sponge-like, fleshy, polymorphous ; the cells 

 irregular in disposition, immersed, and concealed with a 

 contractile non-operculate aperture. 



ALCYONIDIUM. 

 Generic Character-. " Polypidom fleshy, lobed, or crusta- 

 ceous ; cells immersed, pentagonal, with fibro-corneous 

 parietes, the aperture terminal, simple, contractile. Poly- 

 pes ascidian." 



SEA RAGGED STAFF. (A. Gelatinosum, ) Poly- 

 pidom fleshy, cylindrical, slightly compressed, irregularly 

 branched or lobed, smooth. 



Fucus Spcngiosus nodosus, Raii Synop., vol 1, p. 49, 

 no. 42. Alevoniurn, seu fucus nodosus et spongiosus, Ellis' 



