580 CERAMIACEAE. 



beaten rocks between the tide-lines and as epiphytes on other algae, habitats 

 that are not characteristic of the northern G. globulifcra. 



Joulter's Cay, Exuma Chain, Atwood Cay, Caicos Islands, and Great Ragged 

 Island: Massachusetts to the American Virgin Islands and Barbados (?). Type 

 from New York. 



2. Griffithsia tenuis Ag. Sp. Alg. 2: 131. 1828. 



Callithamnion tenue Harv. Ner. Bor.-Am. 3: 130. 1858. 

 Griffithsia thyrsigera (Thwait.) Grun. Alg. Fidschi 8. 1877. 



An antheridial fragment, washed ashore, Berry Islands : Massachusetts and 

 Bermuda to Barbados ; Adriatic Sea ; Ceylon ; Australia ; etc. Type from Venice. 



4. CALLITHAMNION Lyngb. Hydroph. Dan. 123. 1819. 



1. Callithamnion Halliae Collins, in C, H., & S., Phyc. Bor.-Am. 698. 1900. 



Belated to C. corymbosum and C. byssoides, but differs from both in having 

 the main axes uncortieated throughout. 



On other algae at low-water mark, under shelving rocks (and washed ashore), 

 Great Bahama and Exuma Chain : Florida. Type from Key West, Florida. 



5. SEIROSPORA Harv. Phyc. Brit. pi. 21. 1846. 



1. ?Seirospora occidentals Borg. Bot. Tidsskr. 30: 14. /. 8, 9. 1909. 



The scanty fertile material has the triangularly divided tetrasporangia sessile 

 or on one-celled pedicels; paraspores 30-40 w broad, in branching, subterminal tufts; 

 main axes uncortieated throughout. Exuma Chain : American Virgin Islands. Type 

 from sound between St. Thomas and St. Jan. 



6. HALOPLEGMA Mont. Ann. Sci. Nat. Bot. II. 18; 258. 1842. 

 Bhodoplexia Harv. in Hook. Ic. PI. 7: pi. 613. 1844. 



1. Haloplegma Duperreyi spinulosum M. A. Howe, subsp. nov. 



Differs from typical H. Duperreyi Mont, in having a thallus that is beset 

 with numerous rigid subspinescent ramelli usually in twos or threes and 25-140 ix. 

 (2-11 cells) long, the cells of these ramelli mostly 1.5-3 times as long as broad. 



Between the tide-lines on a rock shelf, under an overhang, Cave Cays, Exuma 

 Chain (Howe 3998). 



7. GYMNOTHAMNION J. Ag. Anal. Alg. 27. 1892. 



1. Gymnothamnion elegans (Schousb.) J. Ag. loc. cit. 178. 



Callithamnion elegans Schousb.; Ag. Sp. Alg. 2: 162. 1828; Born. & Thur. 



Not. Alg. 32. pi. 10. 1876. 

 Ptilota Schousboei Born, in Born. & Thur. loc. cit. 34. 

 Plumaria Schousboei Schmitz; Born. Mem. Soc. Sci. Cherbourg 28: 330. 



1892. 

 ? Gymnothamnion bipinnatum Collins & Hervey, Proc. Am. Acad. 53: 139. 



pi. 4. f. 26. 1917. 

 ? Ptilothamnion bipinnatum M. A. Howe, in Britton, Fl. Bermuda 525. 

 1918. 



The main branches are simply pinnate and the opposite ramuli are usually 

 longer than in Bermudian specimens described as G. bipinnatum but not alto- 

 gether dissimilar conditions occur in the Bermudian type and the species is 

 probably the same. The Bahamian specimens, like the Bermudian, appear to 

 bear only tetrasporangia (tripartite), and pending the discovery of antheridia 



