474 BULLETIN OF THE BUREAU OF FISHERIES. 
Plants 0.8 to 2.6 mm. tall, usually 1.5 to 2 mm.; one to many filaments arising from a basal disk; 
cells 7 to 14 mic. in diameter below, 4 to 10 mic. in diameter above, 3 to 5 diameters long below, 4 to 6 
diameters long above; filaments long and straight with rather few long, straight, erect branches, usually 
terminating in a very slender hair; short ramuli, mostly 1 to 3 celled, abundant, scattered, opposite or 
in short secund series, bearing either hairs or terminal sporangia; sporangia also sessile on the branches, 
occupying the places of ramuli, 10 to 12 by 20 to 24 mic.; sexual organs unknown. 
Temperate North Atlantic. 
Fairly abundant on Gracilaria multipartita, G. confervoides, Agardhiella tenera, Petalonia fascia, 
and Padina vickersie on Fort Macon and Shackleford jetties and in harbor, Beaufort, N. C., 
throughout the year. 
This species may be distinguished by its basal disk bearing one or more erect filaments and its long, 
straight branches, which are often subsimple. In the typical form the branches bear short ramuli or 
spores on nearly every cell, and numerous hairs, the hairs not being formed by a gradual tapering of the 
branch but appearing abruptly at the apex of a cell of about the same size as the preceding ones. But 
in some forms the branches are long and tapering, without hairs and with infrequent branching. 
In the Beaufort specimens hairs are lacking and short ramuli are infrequent. In some specimens 
the branches taper gradually to the apices, in some they taper slightly, while in some specimens, similar 
to the preceding ones in other respects, they are nearly of uniform diameter throughout. In the majority 
of cases the filaments are long, straight, and sparingly branched, sometimes being entirely simple; 
sporangia are borne in short secund series on the main branches, usually being lateral and sessile, less 
often terminating longer or shorter ramuli. In these respects the Beaufort specimens resemble 
f. tenuissima Collins (1906, p. 194). From this they differ, however, in that the diameter of the 
filaments is greater and the basal disk is larger, sometimes almost forming a continuous layer of con- 
siderable extent and approaching in this respect f. Juxurians Collins. 
This is the southern limit reported for the species on our coast, but it probably extends farther. 
Acrochetium sp. 
Plants differing from all the above-mentioned species and not certainly referable to any described 
species were found in abundance on Sargassum filipendula, Agardhiella ienera, and, in less amount, on 
Gracilaria confervoides dredged from the coral reef offshore, July and August, 1915. In view, however, 
of our ignorance of the variation of plants belonging to this genus when growing on different hosts or 
under different conditions it has not seemed wise to describe these as a new species. 
Of the seven identified species of this genus found at Beaufort five have been observed 
on only one host—A. hoytii and A. affine on Dictyota dictotoma, A. parvulum on Polysi- 
phonia harveyi, A. corymbijerum on Dasya pedicellata, and A. infestans on hydroids. 
A. dujourit has been observed on Sargassum filupendula and apparently also on Dictyota 
dichotoma, while A. virgatulum has been found on five species of alge, but not on the 
same host occupied by any of the other species of Acrochetium. 
Family 2. GELIDIACE (Kuetzing) Schmitz. 
Frond terete or compressed, usually laterally branched, with fairly evident fila- 
mentous structure and usually thick and firm texture, traversed by a segmented axial 
tube (often indistinct in the older parts), from which arise branched lateral filaments 
composing the cortex; tetrasporangia zonately, cruciately, or triangularly divided, 
grouped in special portions of the thallus or scattered in the outer rind; antheridia 
occurring in a more or less widely expanded layer over the surface of special portions of 
the thallus or forming small, scattered tufts arising from the cortical filaments; 
carpogonia borne beneath the surface on the cortical filaments or laterally on the 
central axis, often occurring in special fertile portions of the thallus; the fertilized 
eggs give rise directly (often after fusion with one or more neighboring—quasi auxiliary 
—cells) to gonimoblasts composed of much-branched, expanded filaments; ends of 
