390 TUFTS COLLEGE STUDIES, VOL. II, No. 3 



'2. Surface of flabellum smooth or sinoothish. 3. A. levis. 



2. Surface of flabellum velutinous, spongy or strigose. 3. 



3. Interior filaments of flabellum moniliform. 2. A. nigricans. 



3. Interior filaments of flabellum cylindrical with basal constrictions. 



4. A. loiigicanlis. 



1. A. RAWSONI (Dickie) Howe, 1907, p. 510, PI. XXX ; P. 

 B.-A., No. 1481. Frond formed of more or less dense, terete, 

 clavate or fusiform, digitate lobes, not developing a flabellum ; 

 filaments cylindrical to subtorulose, always strongly constricted 

 just above a dichotomy, rather thin-walled, 30-70 /A diam.; color 

 rather light green when growing, brownish or blackish when 

 dried. W. I. 



The digitately lobed frond, much resembling some of the 

 common digitate sponges, sufficiently distinguishes this from 

 our other species. The material distributed in P. B.-A., No. 

 770 as A. longicaulis and No. 771 as A. nigricans, was largely 

 A. Rawsoni, but also with some A. nigricans, as now defined. 



2. A. NIGRICANS Decaisne, 1842, p. 96; Howe, 1907, p. 

 508, PI. XXVIII, figs. 8-25 ; A. longicaulis Murray and Boodle, 

 1889, p. 70, PI. CCLXXXVIII, figs. 1-5. Flabellum suborbic- 

 ular to cuneiform, irregularly and obtusely lobed ; coriaceous, 

 sessile or stipitate, from a more or less distinct subterranean 

 rhizome ; filaments very regularly moniliform ; those of the in- 

 terior 50-70 /u, diam., near the surface about 30 p., with closer set 

 constrictions ; sporangia clavate to globose, 350-800X200-350 /*; 

 spores ovoid, pyriform, or elongate-ellipsoidal, 130-300X66-120 

 p.. Color dark brown or blackish. W. I., Fla. Brazil. 



A coarse and unsightly plant, forming dense growths under 

 the surface of the mud in shallow sheltered waters ; the tuber- 

 like rhizome is usually infested with many minute animals. 

 The texture of the flabellum is quite loose, not entirely opaque, 

 when held against the light. 



Forma FULVA Howe, P. B.-A., No. 1480. Flabellum thicker, 

 more spongy ; stipe flatter, broader and less differentiated ; fila- 

 ments coarser, less regularly moniliform, more frequently and 

 divaricately forked ; color more yellowish. With the type. 

 The sporangia noted above for this species were found on an 

 individual of forma fulva. 



3. A. LEVIS Howe, igosa, p. 565, PI. XXIII, fig. i ; PL 

 XXVI, figs. 8-10 ; P. B.-A., No. 1478; A. sordida Murray and 

 Boodle, 1889, p. 70.* Flabellum cuneiform-obovate to reni- 



* A. asarifolia Borgesen, 1908, p. 34, fig. 4, PI. Ill, is hardly to be dis- 

 tinguished from A. levis ; the specimens of the latter distributed as P. 

 B.-A., No. 1478 are not at the fullest development, but other specimens 



