60 REPORT OF COMMISSIONER OF FISH AND FISHERIES. 



found on the sliores of California. It is very widely diffused, being found in nearly 

 all seas. B. hypnoides, wliicli occurs at Key West, passes almost insensibly into B. 

 plumosa, but tbe typical B. hypnoides is not known in New England. 



?DERBESIA, Sol. 



(Named in honor of Prof. Alplionse Derhes, of Marseilles.) 



Fronds green, simple or sliglitly branching, unicellular, or sometimes 

 with cross-partitions at the base of the branches ; fructification con- 

 sisting of ovoidal sporangia containing zoospores, which are of large 

 size and have a hyaline papilla at one end, at the base of which is a 

 circle of cilia j oospores unknown. 



The genus Derhesia was founded by Solier on two Mediterranean species, D. marina 

 and D. Lamourouxii. The position of the genus is doubtful. The Derhesice resemble 

 in habit the more delicate species of Vaucheria and Bryoj)sis, and like them are often 

 unicellular, but it is, however, not uncommon to find at the base of some of the sterile 

 branches a short cell, sei^arated by a wall both from the branch above and the main 

 filament below. A similar cell is always present at the base of the sporangia, and 

 the same cell is found in some species of Vaucheria. Derhesia differs from Bryojjsis in 

 having zoospores provided with a circle of cilia, borne around the base of a terminal 

 hyaline papilla as in (Edogonium. It differs from Vaucheria in not having oospores, so 

 far as is known. The zoospores of Derhesia, according to Solier, germinate at once 

 and are apparently of a non-sexual character, so that we may expect that hereafter 

 either oospores or conjugating zoospores will be found. As we have said, the zoospores 

 bear a striking resemblance to those of (Edogonium, and perhaps the relationship to 

 the last-named genus is closer than has usually been supposed. In this connection 

 it should be mentioned that, in the formation of the cells sometimes found at the base 

 of the branches, the cell-wall ruptures in the same way as in (Edogonium, and if we 

 do not have the same rings forming a cap at the end of the cells as in (Edogonium it 

 may be because in Derhesia the formation of new cells is very limited. 



D. TENUISSTMA (De ^^ot.), Crouan. {B. marina, Solier, Ann. Sci. :N'at., 

 3 serie, Yol. YII, p. 158, PI. 9, Figs. 1-17.— Bryopsistenuissima, DeNot., 

 Fl. Capr.— D. tenuissima, Crouan, Florule du Finistere, non B. marina, 

 Crouan, Algues Marines du Finistere, Xo. SdS.—Chlorodesmis vaucliericv- 

 formis, Harv., Ner. Am. Bor., Part III, p. 30, PL 40 c.) PI. IV, Fig. 4. 



Filaments tufted, bright green, one to two inches long, .04'""' in 

 diameter ; branches few, erect, constricted, and often with a cuboidal 

 cell at the base; sporangia on short branches, ovoidal or pyriform, 

 .09-.12'"'" broad by .20-.30""" long, resting on a cuboidal basal cell; spores 

 large, few, about 15 in number. 



Forming tufts on algse. 



Eel Pond Bridge, Wood's Holl, Mass.; Key West; Europe. 



We have found this species but once on our coast, in May, 187G. With us it is 

 apparently rare, but the species is not uncommon in some parts of Europe, especially 

 on the shores of the Mediterranean. Our form is very well developed and the 

 sporangia are rather longer than in the European specimens which we have seen. 



