328 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 
which occurs in the same area but on the coasts of the 
Trish Sea also. B. hypnoides is recorded from the Isle of 
Man and Puffin Island, Anglesea, but requires confirma- 
tion; B. plumosa is fairly common in rock pools in the 
L.M.B.C. area. 
Il. DERBESIACEZ. 
This order also includes only one genus, Derbesia, with 
about 8 species, according to Wille (Engler and Prantl, 
Pflanzen-familien). The thallus is simple, irregularly or 
dichotomously branched, and produces spherical swarm- 
spores in lateral zoosporangia. Hach zoospore is provided 
with a circlet of cilia, surrounding the bluntly pointed 
hyaline apex. 
Derbesia tenwissima, Crn., is recorded from the English 
Channel, but it has not as yet been discovered in the 
L:M.B.C. area. 
Ill. VAUCHERIACEA. 
This order also is represented by only one genus, 
Vaucherta, and embraces about 25 species, which are 
inhabitants of fresh or brackish water. Whilst vegetatively 
not unlike Derbesia, Vaucheria differs markedly in its 
methods of reproduction from the rest of the Siphonee. 
In addition to considerable powers of vegetative multipli- 
cation, solitary zoospores (zooccenocytes) are developed in 
sporangia formed by the abstriction of the terminal por- 
tions of vegetative branches. Sexual organs in the form 
of ovoid oogonia and filamentous antheridia also occur as 
lateral branches of the filamentous thallus. Fertilisation 
of the solitary ovum takes place within the oogonium, the 
oosperm developing into a new Vaucheria filament after a 
period of hibernation. 
Five species, with several varieties, are found on British 
