20 ¥. E. FRITSCH. 
biseriate arrangement. The same thing may more rarely take place in the expanded 
part of the thallus, which occasionally exhibits prominent constrictions. In spite of 
all these irregularities there is a very sensible and gradual widening of the plant 
after the first permanent longitudinal divisions set in. 
In many of the plants the broadening out of the thallus did not go very 
far, so that the whole plant had a filiform appearance, with a length many times 
exceeding its breadth. This, and the very gradual widening of the stipe into 
the thallus, appear, according to Imhauser (“ Entwicklungsgesch. u. Formenkreis v. 
Prasiola” Flora, 1889, Heft 3, Diss. Marburg, 1889, pp. 47 and 55) to be the two most 
prominent characteristics of the species. These two characters are also well shown 
in exsiccata of 2. calophylla (from Tristan d’Acunha, Hb. Dickie) preserved in the 
British Museum, although the specimens are not as elongated as those from Winter 
Harbour. 
In the expanded thallus (text-figure J) it was often not easy to recognise the 
longitudinal seriation of the cells, referred to in many descriptions of the species 
(Imhiiuser, op. cit.; De Toni, op. cit.; Rabenhorst, op. cit.; F. 8. Collins, “ Green Algee 
of N. America,” Tuft’s College Studies, Scient. series, IL, No. 3, 1909, p. 219). The 
cells were regularly arranged in groups of four and were often practically equi- 
distant, so that an areolation, such as that in P. crispa, was not manifest; but 
this grouping of the cells was frequently interrupted owing to the cells in adjacent 
parts of the thallus showing a slightly different orientation. The cells in the 
expanded thallus were often almost square, the cell-contents measuring 5-6 x 5-6 p. 
Some of the larger thalli attamed a length of 2 cm. and a breadth of about 
a millimetre (at their widest point). The specimens from Granite Harbour were 
much shorter than those from the other habitat. 
No reproductive stages were observed, but intermingled with the other growth 
on the stones from Winter Harbour were Prasiola-packets, which did not differ in 
any respect from those of P. crispa. Presumably they belonged to P. calophylla. 
COIN WG Ai as 
MESOTAINIACE. 
Genus Pentum Bréb. 
14. PENIUM sp. 
(Pl Ly digs, 455846;) 
Cellulis subcylindricis vel modice ellipsoideis, latitudine circa duplo longioribus, 
polis rotundato-deplanatis, constrictione modica in media parte cellule munitis ; 
membrana cellule levis et hyalina, modice sed equaliter incrassata; contentu 
