4 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 26 



slightly recurved, blunt-tipped, simple or provided with a few short 

 adaxial branchlets; gland cells absent; tetrasporangia ellipsoid, 12-17 /x, 

 surrounded by a thick gelatinous envelope about 5 /a thick, variously 

 situated, terminal on primary lateral branchlets and (or) adaxial on 

 these, sessile or pedicellate; sexual reproduction unknown. 



Type : Holotype is a Hornemann collection from Herb. Schousboe, 

 probably in the Agardh Herbarium, Lund, Sweden. 



Type locality: "Ad Tingin" = Tangiers, North Africa. 



Pacific distribution: California — D. 5507, Santa Catalina 

 Island. Revillagigedo Arch. — D. 13754, intertidal, Binners Cove, Isla 

 Socorro; Mason 32, Isla Clarion. Galapagos Arch. — Taylor 34-120, Isla 

 Isabel. 



This seems to be a widespread but inconspicuous plant of warm 

 waters in the Atlantic and Pacific, easily recognized by its tetrasporangia 

 which are at least partially terminal on the determinate laterals. 



It should be noted that Yamada and Tanaka (1934) have described 

 a plant as Plumaria ramosa which shows many resemblances to the 

 present species and should be taken into account in further studies of 

 this group. 



Platythamnion 



This artificial genus, set up by J. G. Agardh (1892) based upon 

 P. heteromorphum and P. orbigniana, and elaborated by Kylin (1925), 

 segregates several species from Antithamnion on the basis of the whorls 

 of four determinate branches from each main axial cell in which one 

 opposite pair of each whorl is much smaller than the other. The genus 

 merges with Antithamnion in the distichous species A. plumulum which 

 in Europe and in Japan produces a partially tetrastichous variety (A. 

 plumulum var. crispum) that is almost identical with the Pacific plant 

 known as Platythamnion pectinatum. A. plumulum var. crispum appar- 

 ently differs from Platythamnion pectinatum only in that the opposite 

 pairs of dwarf lateral branchlets are of inconsistent occurrence, and 

 do not, even when in maximum development, extend regularly to the 

 tips of the main axes. Feldmann (1937) treated A. plumulum var. 

 crispum as Platythamnion crispum, but G. Feldmann-Mazoyer (1940) 

 returned it to Antithamnion in agreement with Daines (1913) who 

 contended that the identity of the development of the carpogonial 

 branch and the gonimoblast in Antithamnion and Platythamnion was 

 such that the vegetative differences were not sufficient to justify generic 

 distinction. 



Recently, Sundene (1959) has cultured and crossed strains of A. 

 plumulum and shown that a distichous Plymouth strain and a tetra- 

 stichous Oslofjord strain are intersterile. 



The nomenclatural problems surrounding Platythamnion have been 



