92 COLLINS AND HERVEY. 



of which we have examined several specimens, belongs under D. 

 ciliata. Agardh, 1848, p. 94, says of D. crenulata "margine tenui 

 dentibus brevissimis late triangularibus initio fere serrato, demum 

 dentato aut crenato." Harvey, 1852, says "The margin is undulated, 

 and closely eroso-denticulate, or jagged with unequal, deltoid or subu- 

 late, tooth-like processes." In the Bermuda plants the margin is 

 quite even, and the teeth are of uniform size and never very closely 

 set. We have, however, seen a specimen of D. crenulata from the 

 Suhr herbarium "West Indien," that fully agrees with Agardh's 

 and Harvey's descriptions. In the Bermuda material of this species 

 confervoid rhizoidal filaments arise from the lower part of the main 

 axis of the frond, often forming a dense, continuous mass for several 

 cm. ; proliferations are few and insignificant. Antheridia and oogonia 

 were found on specimens collected in February, tetrasporangia on 

 specimens collected in July. 



8. D. DENTATA Lamouroux, 1809, p. 331; Kiitzing, 1859, p. 15, 

 PI. XXXV, fig. I; D. Mertensii (Mart.) Kiitzing, 1859, p. 15, PI. 

 XXXVI, fig. I; Ulna Mertensii Martius, 1826, p. 21; 1827, PI. I; 

 P. B.-A., No. 1926; D. Brongniartii J. G. Agardh, 1841, p. 5; Kiitzing, 

 1859, p. 15, PI. XXXV, fig. II; D. subdentata Kiitzing, 1859, p. 14, 

 PI. XXXIII, fig. II. Kemp, as D. crenulata, in part; Gravelly Bay, 

 Jan., Hervey, Aug., Collins; Hungry Bay, July, Collins. J. G. 

 Agardh, 1880, p. 98, gives D. Mertensii as a synonym of D. Brong- 

 niartii, mentioning D. subdentata without expressing an opinion as to 

 whether it should be referred to D. dentata or D. Brongniartii; later, 

 1894, p. 70, he recognizes D. dentata, D. Mertensii and D. Brongniartii 

 as distinct species. Hauck, 1888, p. 466, unites all four under the 

 oldest name, D. dentata, as it seems to us rightly. The distinctive 

 characters are found in the greater or less distinctness of the axis and 

 branches, and in the character of the terminal segments. In the 

 abundant material we found in Bermuda, there were individuals with 

 the primary axis narrower and firmer than the lateral segments, and 

 others, apparently mostly younger individuals, in which all was 

 uniformly membranaceous. Typical D. dentata has segments ending 

 in acute, spinous tips; typical D. Mertensii has segments short- 

 cuneate, with truncate or emarginate tips. It is not uncommon to 

 find both these types on the same individual. In comparing the 

 vegetative structure of D. dentata with that of D. dickotoma, as de- 

 scribed by Reinke, 1878, several points are to be noted. The main 

 axis is thick, and somewhat flattened, but can hardly be described as 

 a " rundtrieb." In old plants, there grow from this, for a distance of 



