132 



encrusting stones and foriiiinn; its cells like a Fluslra, in largo 

 circuinsoribed patches. The first appearance of its rising 

 into a laniellated form, is the production of detached ridges 

 and papillary eminences, as tliese become more elevated they 

 assmne the form described above. 



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

 formed, in the first place very delicately, and afterwards 

 completed and strengthened by depositions of calcareous 

 uialter. 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 polypidom is frequently marked b}' ridges, 

 which indicate the extent of the various enlargeuients ; and 

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

 gelatinous effusion, 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 encrnsling 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 tliat the growth 

 is effected here as it is in Lepraiia, F/ustra, &c. Tl)e cells, 

 which are superficial and on both sides of the leaf whea 

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

 They present three varieties of appearance the first of which. 

 is the semi-gelalinous or p»dpy state, the second where the 

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

 third is the confused appearance produced by the partial 

 and complete obliteration of the cells. 



ALCY0NIDULJ2. 



Polypidoms sponge-like, fleshy, polymorphous ; the cells 

 irregular in disposition, imuierseii, and concealed with a 

 contractile non-operculate aperture. 



ALCYONIDIUM. 

 Generic Characler: " Pulypidom 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 Spongiosus nodosus, Raii Synop., vol 1, p. 49, 

 no. 42. AlcNonium, seu fucus uodosus el spongiosus, Ellis' 



