508 Howe: Phycological studies 



merited on the characters of the original specimens of Avrainvillea 

 nigricans Decaisne and Rhipilia longicaiilis Kiitz. Since that time 

 we have enjoyed the opportunity of seeing again Hving plants of 

 this genus in Porto Rico and in Jamaica, and have arrived at con- 

 clusions that are, to us, more satisfactory as to the number of spe- 

 cies that are represented in the West Indian waters, in so far as 

 one may judge of the matter from the material now at hand. We 

 therefore venture to give below a diagnosis of the genus, a key to 

 the American species, and a synoptical account of the four species 

 that we recognize. 



Avrainvillea Decaisne, Ann. Sci. Nat. II. i8 : io8. 1842 

 Fradelia Chauvin, Recherches 124. 1842. 

 Chloroplegma Zanard. Mem. R. 1st. Ven. 7: 290. 1858. 



Thallus fusco-nigrescent, tawny-green, or olivaceous, usually 

 flabelliform and stipitate, more rarely difform or irregularly digi- 

 tate, destitute of calcareous incrustation, composed of dichotomous 

 interwoven cylindrical, torulose, or moniliform threads, these nearly 

 similar throughout, being without specialized corticating branches 

 and without fibular processes. Stipe, when differentiated, simple 

 or sometimes forked, terete or flattened. Flabellum suborbicular, 

 reniform-cordate, or cuneiform, or (in A. Rmvsoni) deficient, rarely 

 zonate. Rhizoids in an irregularly bulbous mass or sometimes 

 forming a rhizome. Sporangia (known only in A. nigricans) ter- 

 minal on filaments exserted from surface of flabellum, containing a 

 few (1-8) spores (aplanospores ?). All species marine. 



Type species, Avrainvillea nigricans Decaisne. 



Key to the American species 



Thallus eventually developing a flabellum (usually stipitate). 



Fusco-nigrescent or tawny-green ; surface subvelutinous, minutely spongiose, or 

 strigose : filaments of flabellum 28-70// in diameter. 

 Filaments of flabellum moniliform. i- A. nigricans. 



Filaments of flabellum cylindrical with a strong constriction at base of each 

 branch, rarely subtorulose. 2. A. lofigicauhs. 



■ Olivaceous or cinereous ; surface smooth and compact ; filaments of surface of 

 flabellum 6-24,^ in diameter. 4. A. levis. 



Thallus not developing a flabellum, forming more or less digitate, sometimes capitate 

 lobes, these commonly very irregular in form, and often branching, diftluent, or 

 anastomosing. 3- ^- Kawsoni. 



I. Avrainvillea nigricans Descaisne, Ann. Sci. Nat. II. i8 : 

 1842.— M. A. Howe, Bull. Torrey Club 32: 567,568. 1905. 

 Fradelia fnliginosa Chauvin, Recherches 124. 1842. 



