ULVACE^. 61 



Hab. Key West, W.H.H., Prof. Tuomey. (No. 103). (v. v.) 



Fronds at first globose, like tubers, heaped together, hollow and empty or filled with 

 sea-water, attached to the rock and to each other by a few short, rooting processes ; at 

 length irregularly torn, and then forming expanded, cartilaginous, or skinlike coarsely 

 reticulated membranes. The membrane is wholly composed of a single layer of large, 

 globose, or by mutual compression hexagonal cells, which closely cohere by their sides, 

 leaving the convex ends of the cell free, and these form the surface of the membrane, 

 which when dry resembles a piece of fish skin, or a miniature honeycomb. When the 

 cells have been separated, each is seen to be marked at the line of junction by a double 

 row of circular discs. In full grown cells the primordial utricle is easily separable from 

 the outer cell-wall, and contains a green, granular endochrome ; from which, by cell- 

 division, four new cells are formed, and thus the frond extends by repeated quadrisection 

 of its component cells. The cell-wall is very tough and semifibrous in texture, more 

 like an animal than a vegetable membrane ; and I have seen hairlike processes issue 

 from it internally, analogous perhaps to the fibrous processes of the membrane of Caulerpa. 

 I cannot say whether this be a constant character. It was observed in specimens from 

 the Pacific brought home in spirit, and cannot be readily ascertained from dried specimens. 



Plate XLIV. B. Fig. 1. DiCTYOSPH^Ru/auMfosa, the natural size. Fig. 2. Portion 

 of the surface, showing the division of the cells. Fig. 3. One of the cells of which the 

 frond is composed, removed ; the latter figures magnijied. 



Order IY.— ULVACE^. 



Grev. Alg. Brit. p. 168. Hooh Br. Fl. 2, p. 309. Harv. Man. p. 211. /. Ag. 

 Alg. Medit. p. 14. Endl. 3rd Suppl. p. 18. Ulvacece et Enter omorpheoe, Kiitz. 

 Spec. Alg. pp. 471-475. 



Diagnosis. Green or purple, marine or fresh water Algas, composed of small, poly- 

 gonal or quadrate cells, forming expanded membranes or membranous sacs or tubes ; 

 rarely arranged in filaments. Fructification, zoospores formed in the cells of the frond. 



Natural character. Root a small disc, or point of attachment. Frond formed of 

 small, often very minute, roundish, quadrate or polygonal cellules cohering together 

 into thin, filmy membranes, of no very definite form, and either expanded into broad 

 leaves, contracted into narrow ribbons, or forming tubes which are either simple or 

 branched. In those of lowest organization, such as Tetraspora, the frond is of a nature 

 so loosely gelatinous that it can only by courtesy be called a membrane, and the cells 

 which give it consistency are widely separated by transparent jelly. In Prasiola the 



