134 COLLINS AND HEEVET. 



duced by the lowest cell of an erect filament. The plant grew on 

 the top of sand-covered rocks, covered at high tide; the coral sand 

 sifted in among the alga, forming a dense fibrous mass. 



Ceramothamnion Richards. 



C. CoDii Richards, 1901, p. 264, PI. XXI; P. B.-A., No. 1899; 

 Plate III, fig. 22; plate IV, fig. 23. Common on Codium tomentosum 

 and other species of Codium all about the islands, at all times of the 

 year, ahnost always in abundant fruit. It was once found on Lauren- 

 da cervicornis. A few notes can be added to the quite full description 

 of Richards. He observed only a single ripe tetrasporangiiun at a 

 node; we have foimd not uncommonly two, rarely three, in one 

 instance four, of apparently equal age, side by side; branches occa- 

 sionally occur independently of the polyspores; we have found organs 

 quite agreeing with his figures of the latter, but also similar organs, 

 larger, up to 160 n diam., spherical, containing up to 45 spores, and in 

 appearance quite indistinguishable from cystocarps of Ceramiumy 

 Against the identification of these organs as cystocarps must be 

 reckoned our failure to discover anything like procarps, and the 

 question must be left open. The rhizoids offer some interesting 

 peculiarities, doubtless due to adaptation to their position, between 

 the closely-packed utricles of the host; at first terete, they soon 

 become flattened, and often two or more unite laterally, in a mem- 

 branous expansion, which may be as much as 10 cells wide. In one 

 case three rhizoids from one individual imited with two from another 

 to form one membrane. The cross walls in these rhizoidal membranes 

 are often much oblique, and the arrangement of the cells reminds one 

 somewhat of that in the leaf of a moss. See Figures 22 and 23. 

 The material from which this species was described was collected in 

 Bermuda in 1898 and 1899; the only other record of its occurrence 

 is at Barbados, Vickers, 1905, p. 65. 



Geiffithsia Agardh. 



1. Vegetative cells cylindrical throughout. 1. G. tenuis. 



1. Lower cells subcylindrical, upper ovoid. 2. G. Schousboei. 



1. All cells subspherical. 3. G. momlis. 



17 Schiller, 1913, has made extensive observations on organs of this char- 

 acter in genera alMed to Ceramothamnion, and he reports that in every case 

 they were accompanied by tetraspores of normal character on the same 

 individual. This is not the case with this species. 



