96 COLLINS AND HERVEY. 



FAMILY HELMINTHOCLADIACEAE. 

 ACROCHAETIUM Nageli. 



A conservative course has been followed by us in regard to the 

 plants belonging to this genus. No such richness of new forms has 

 been found here as by Borgesen in the Danish West Indies, but we 

 cannot claim to have made as thorough a study as he has, and it is 

 very unlikely that all the Bermuda forms have been discovered and 

 listed. We include under Acrochaetium the marine species formerly 

 passing under Chantransia, many of which have recently been juggled 

 back and forth, only too often. 



1. Original spore remaining manifest at base of filament. 



1. Original spore not distinguishable. 5. 



2. Basal cell with descending endophytic and erect free filaments. 



2. No descending endophytic filaments. 4. 



3. Cells 8-10 M diam., 4-5 diam. long. 3. A. corymbiferum. 



3. Cells 12-14 M diam., 2-3 diam. long. 4. A. barbadense. 



4. Cells short, subspherical. 2. A. crassipes. 



4. Cells long, cylindrical. 1. A. Dufourii. 



5. Frond arising from a disk. 8. A. Thuretii. 



5. Frond not arising from a disk. 6. 



6. Horizontal filaments on surface of host. 7. 



6. Horizontal filaments endophytic only. 9. A. Hypnae. 



7. Horizontal filaments producing endophytic branches. 



7. A. Nemalionis. 

 7. Horizontal filaments without endophytic branches. 



8. Erect filaments 6-12 diam. 6. A. Sagraeanum. 



8. Erect filaments 4-5 M diam. 5. A. leptonema. 



1. A. DUFOURII Collins, P. B.-A., No. 1594; Chantransia Dufourii 

 Collins, 1911, p. 187; P. B.-A., No. 2087. On Dictyota ciliata, Hungry 

 Bay, Dec., Hervey. Forming a dense fringe on the edge of the host. 

 The basal cell (original spore) remains distinct, attached to the host 

 by a circular disk, of diameter larger than that of the cell. This 

 development is of the same character as that in Chantransia collopoda 

 Rosenvinge, 1909, p. 81, but on a smaller scale; it is found also in 

 another Bermuda species, A. crassipes. 



2. A. CRASSIPES Borgesen, 1915, p. 20, fig. 11; Chantransia cras- 

 sipes Borgesen, 1909, p. 1, fig. 1; P. B.-A., No. 2033. On Ceramium 

 clavulatum and Polysiphonia ferulacea, St. David's Island, Feb., and 

 on CaUithamnion Hookeri, Gravelly Bay, April, Hervey. 



