Additional Notes on Marine Pyrenomycetes. 185 
The presence of asci at all stages of growth points to a 
successive development of these bodies as in Mycosplitzrella. They 
are clavate or fusiform and curved (Fig. 1, 4) with thin tenacious 
walls within which the ascospores are arranged usually in two sets 
of four, dovetailed together. The latter are also fusiform, curved, 
thick-walled, and 3-septate, with the terminal cells longer than the 
middle two. All become slightly coloured at maturity. 
This species is very similar to that occurring on Ascophyllum 
nodosum. However, there is no doubt of its being a separate 
species. Not only does it differ from the latter in possessing distinctly 
smaller perithecia, asci and ascospores ; its mycelium spreads less 
extensively, does little damage to its host and bears perithecia more 
deeply immersed. This is also borne out by its distribution. 
Although the two belts of Ascophyllum and of Pelvetia frequently 
stretch along the beach for a considerable distance in close, almost 
parallel lines, and the thalli of the former become covered with 
the black patches indicating attack by its particular species of 
Orcadia ; so far, not only has no corresponding infection of the 
latter been observed, but the thalli on which Orcadia pelvetiana 
was found, were collected on rocks near which no Ascophyllum 
grew. 
The reasons for the formation of the genus Orcadia have been 
already discussed. 
DlDYMOSPHJERIA PELVETIANA NOV. SP. (FlO. 2, 1-4). 
Mycelium diffusion, perithecia simplicia, sparsa, minuta, circa 
90-115// diam., globosa, membranacea, immersa tota, ostiolo 
brevissimo pseudo-clypeum perfringente: asci crebri, cylindracei 
vel apicibus attenuatis, 55-75// x 9-11/x, parietibus tenuibus, octo- 
spori; paraphyses filiformes vel raro in duos tresve ramos, divisse; 
sporidia disticha, fusiformia, 18-24//, x 5-6//, 1-septata, primo 
hyalina, demum flavescentia, leviter constricts. 
Hab. In thallo vivo Pelvetiae canaliculate, Orkney and 
Solent. 
Didymosphceria was found first on attached thalli in the Orkneys 
and later on sea-borne material in the Solent, thus indicating the 
probability of a fairly wide distribution, although the writer has 
failed to obtain it on fixed plants on the South Coast. The limited 
examination, possible so far, does not, however, preclude the 
possibility of its occurrence there. 
