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 i 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 multipartite, G. confervoides , Agardhiella tenera, Petalonia fascia, 

 and Padina vickersia 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. tenuisnma 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. luxuriant Collins. 



-This is the southern limit reported for the species on our coast, but it probably extends farther. 



Acrochaetium 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 tenera, 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. corymbiferum on Dasya pedicellate, and A. infestans on hydroids. 

 A . dufourii has been observed on Sargassum filipendula and apparently also on Dictyota 

 dichotoma, while A . mrgatulum has been found on five species of algae, but not on the 

 same host occupied by any of the other species of Acrochaetium. 



Family 2. GELIDIACE^E (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 



;lls) to gonimoblasts composed of much-branched, expanded filaments; ends of 



