134 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 12 



AGROGHAETIUM Nageli,1861 



Filamentous, rose red ; from a basal holdfast cell, a disk, or from de- 

 cumbent filaments giving rise to simple or branching uniseriate erect fila- 

 ments, which may terminate in hairs; chromatophores one to few in each 

 cell, stellate, ribbonlike or disciform ; sporangia terminal or lateral, usually 

 monosporous ; sexual reproduction infrequent, by scattered spermatangia 

 and lateral or intercalary carpogonia ; cystocarps forming short filaments 

 direct from the carpogonium, the outer cells forming the carpospores. 



KEY TO SPECIES 



1. Plant without an extensive creeping system, the erect portion 

 dominant A. Daviesii 



1. Plant chiefly creeping, with but very short erect branches pro- 

 truding little beyond the surface of the host ... A. penetrale 



Acrochaetium Daviesii (Dillw^n) Nageli 



Drew 1928, p. 172 (as Rhodochorton Daviesii). 



These plants agree tolerably with the description of western repre- 

 sentatives of the species, but show a seemingly more extensive disklike 

 base of laterally approximated filaments. 



Mexico: Is. Revilla Gigedo, epiphytic on Caulerpa from the lower 

 tide pools and sublittoral of Sulphur Bay, I. Clarion, no. 34-52, 5 Jan. 

 1934. 



Acrochaetium penetrale (Drew) n. comb., prox. 



Drew 1928, p. 187, pi. 44, figs. 57, 58 (as Rhodochorton penetrale). 



These plants are abundant in the somewhat chitinous branches of 

 Zoobotrys. The intramatrical ramification is very extensive and the cells 

 mostly 4.5-8.5 fi diam., and 2-3 diameters long, but very variable. The 

 emergent branches are small and often simple, but may show 1-4 short 

 erect tapering branchlets. As the spores seen were doubtfully mature, the 

 specific assignment is provisional. Since the species has single chrom.ato- 

 phores and reproduces by monospores, the writer prefers to remove it to 

 the genus Acrochaetium, which he maintains, but which Drew (loc. cit.) 

 considered a synonym of Rhodochorton. 



Costa Rica: dredged as growing in Zoobotrys in Port Parker, no. 

 39-89, 25 Mar. 1939. 



