40 DASYCLADE^. 



really the growing point of the frond. I regard the disc as being properly a whorl of 

 sporangia, united by their edges ; each radiating cell constituting a sporangium. The 

 discs, after they have developed spores, are deciduous ; and new ones are successively 

 formed, one above the other, as the stipe lengthens. 



1. AcETABULARiA crmulata, Lamour. ; margin of the peltate disc minutely crenu- 

 late ; the cells apiculate (when young). Lam. Pol. Flea;, p. 6, Tab. 8, Jig. 1. Kutz., 

 Sp. Alg.p. 510. (Tab. XLII. A.) 



Hab, Eocks and corals, within tide marks, on the Florida reefs. Key West, W.H.ff., 



Prof. Tuomey (v. v.) 



Root minute, discoid. Fronds scattered or tufted, two or three inches high, consisting 

 of a slender, setaceous stipes, thinly coated with carbonate of lime, and bearing at its 

 summit a peltate disc or cup, radiated like an agaric, and formed of clavato-cylindrical 

 cells cohering by their edges, and filled with green endochrome. The stipes, when 

 deprived of its lime by maceration in acid, forms a membranous, cylindrical tube, des- 

 titute of markings, slightly enlarged upwards, having near its summit one, two, three, 

 or more (according to age) annular swellings, from which issue whorls of very delicate, 

 polychotomous, byssoid ramelli, and terminating in the first formed disc, from whose 

 centre a pencil of similar byssoid fibres is produced. In further growth, the stipes 

 proceeds through the first disc upwards for a distance of 1-2 lines, where another an- 

 nulus emits a second whorl of filaments, above which a second disc is formed ; and thus, 

 by successive apical growths new discs succeed each other, the older falling off as the 

 younger are formed. In old specimens, therefore, you find the upper part of the stipe 

 furnished with 4-5 or more annuli, marked with scars of the fallen ramelli and discs. 

 In full grown specimens, the peltate disc, or circle of sporongia, is nearly half-an-inch 

 in diameter. At first the matter contained in its cells is fluid and homogeneous. 

 Eventually nuclei are formed in it, and the contents of each cell is converted into 

 numerous globose spores, the whole endochrome being consumed in the process. The 

 cell-wall of the stipe is thick and concentrically striate. 



This species very closely resembles A. Mediterranean from which it is distinguished 

 by the minutely crenulate margin of the disc. In A. Mediterranea the margin is 

 quite entire. 



Plate XLII. A. Fig. 1. Acetabularia crenulata ; the natural size. Fig. 2. Apex 

 of a young frond, before the development of the peltate disc. Fig. 3. A young disc, 

 Avithin which is a pencil of byssoid fibres. Fig. 4. A mature disc. Fig. 5. Apex of 

 one of the radiant cells, from a young disc in which they are mucronate. Fig. 6. One 

 of the radiant cells of a mature disc, converted into a sporangium, and full of spores. 

 Fig. 7- Spores from the same : all the latter figures magnified. 



