MARINE ALGM. OF BEAUFORT, N. C. 469 



sporangia and sexual organs on the same or different individuals; antheridia and 

 carpogonia ori the same or different individuals. 



About no species, fresh water and marine, in temperate and tropical regions. 



Genus Acrochastium Naegeli. 

 Acrochaetium, Naegeli, 1861, p. 402. 

 Trentepohlia, Farlow, 1882, p. 108. 

 Chantransia, De Toni, 1897, p. 67. 



Thallus filamentous, segmented, monosiphonous, irregularly branched, increasing 

 in length by transverse division of the apical cell, branches often terminating in hairs; 

 asexual propagation by monospores, occasionally by dispores, tetraspores, or polyspores, 

 sporangia occurring singly or in tufts, lateral and sessile on the branches or terminal on 

 short ramuli ; sexual reproduction by eggs borne in carpogonia, and spermatia ; antheridia 

 borne in tufts at the apices of short branches ; carpogonia borne singly at the apices of 

 one to three celled branches; sporocarp naked, bearing a tuft of filaments whose ter- 

 minal cells form carpospores; sporangia and sexual organs borne on the same or 

 different individuals ; monoecious or dioecious ; sexual reproduction apparently lacking 

 in some species. 



About 60 species, marine and fresh water. 



This genus has had a varied nomenclature. Originally described as Acrochaetium, 

 it has been called Chantransia by many authors. For a time the group, as now reco- 

 nized, was separated into two genera the species with sexual fruit being placed under 

 Chantransia and those with sexual fruit unknown being referred to Acrochaetium. It 

 is now generally agreed that this distinction is not valid, but there is still disagreement 

 as to the proper name for the genus. As was pointed out by Howe (i9i4a, p. 83), the 

 name Chantransia has been used for several other forms and is, moreover, a violation 

 of all the codes of nomenclature. The name Acrochaetium is therefore to be preferred, 

 both because of its priority and because it is less likely to cause confusion. 



Some of the species are distinguished with ease, but others are separated by incon- 

 spicuous, apparently intergrading, characters, and are determined with great difficulty. 

 It is often impossible to decide with certainty to what species a single given plant 

 should be referred. 



KEY TO SPECIES. 



a. Plants growing in hydroids 6. A. infestans (p. 473). 



aa. Plants growing on or in other algae b. 



b. Upright filaments arising from an external basal disk 7. A . virgatulum (p. 473). 



bb. Upright filaments arising in part from an external or internal basal filament c. 



c. Basal filament entirely internal, original basal cell conspicuous, sporangia, antheridia 



and carpogonia borne on different plants 5. A . corymbiferum (p. 473). 



cc. Basal filament mostly external, original- basal cell inconspicuous, sporangia, antheridia 



and carpogonia borne on the same plants 4. A . affine (p. 471). 



bbb. Upright filaments arising from a single basal cell or from a few secondary basal cells d. 



d. Plants not visible to naked eye . : i. A . parvulum (p. 470). 



dd. Plants visible to naked eye as a fine velvety fringe or mat e. 



e. Basal cell pear shaped, penetrating the host to a depth of 12 to 20 mic. . . .4. A. affine (p. 471). 

 ee. Basal cell spherical or nearly so, 12 to 25 mic. in diameter, not conspicuously 

 penetrating the host, usually bearing several upright filaments, branches often 



elongated and tapering toward apices 3. A . hoytii (p. 470). 



eee. Basal cell spherical, 5 to 8 mic. in diameter, superficial, usually bearing a single 

 upright filament, branches not greatly elongated, not tapering toward apices 



2 . A . dufourii (p. 470). 



