Howe : Phycological studies 573 



obscured by the very numerous decurrent filaments, its cells 2-8 

 times longer than broad ; peripheral filaments 4-6 times dichot- 

 omous, beautifully fastigiate, 0.5-0.8 mm. long, scarcely con- 

 stricted at the joints, 5-6 /j. in diameter, the more peripheral cells 

 2-5 times as long as broad : carpogonial branch simple, consisting 

 of 5—19 subspherical or somewhat discoid cells in a single series, 

 its apex slightly deflexed and terminating in the much elongated, 

 curved or nearly straight trichogyne ; auxiliary- cell branches 

 numerous, consisting of 5-9 enlarged subspherical or oblate- 

 ellipsoidal cells near base, terminating in a multiarticulate pro- 

 longation similar to that of the other peripheral filaments or often 

 shorter ; auxiliary-cell occupying the middle of the enlarged por- 

 tion of the branch and having little more than half the diameter of 

 the two immediately adjacent cells, the latter much inflated, rich 

 in contents, 15—30// in transverse diameter: cystocarps 0.1 2-0.24 

 mm. in diameter, often 2— 4-lobed : antheridia and tetrasporangia 

 unknown. [Plate 28; plate 29, figures 12-26.] 



On rocks in 3 m. of water (low tide), Castle Harbor, Bermuda : 

 no. 315, type (6 July 1900, M. A. H.); also a floating fragment 

 at Spanish Point, Bermuda, no. ig8 . 



Dudresnaya crassa is nearest allied to D. coccinca (Ag.) Crouan 

 in the structure of the carpogonial branch and the auxiliary-cell 

 apparatus and in the elongated cells of the peripheral filaments, 

 but is very different in size and habit, in the obtuse ultimate 

 branches which have nearly the diameter of the primary, in having 

 its peripheral filaments 2-4 times as long as in D. coccinea, and in 

 the highly specialized auxiliary-cell, which is always much smaller 

 than the conspicuously enlarged adjacent cells. Thuret states* 

 that in D. coccinea the branches which bear the antheridia occur 

 on the same plants that bear the cystocarps ; in D. crassa, the 

 antheridia have been searched for in vain on the cystocarpic indi- 

 viduals — the only sort collected — and the species is believed to 

 be dioicous. In its dense habit of branching, the species bears a 

 closer superficial resemblance to D. purpnrifera J. Ag., though the 

 branches are obtuse and coarser ; however, in structure of the 

 carpogonial branch and the auxiliary-cell apparatus f and in the 

 character of the peripheral filaments, it differs so widely that no 

 detailed comparison is necessary. 



* Bornet & Thuret, Notes Algologiques, 36. 1876. 



•fSee Oltmanns, Morphologie und Biologie der Algen 1 : 688-691. f. 441a, 44/. 

 1904. 



