538 MR. W. WEST AND PROF. G. S. WEST ON 
Genus Micrastertas, Agh. 
4. M. Murrayi, sp. n. (PI. 15. figs. 1, 2.) 
M. mediocre, tam longa quam lata, profundissime constricta, 
sinu acutangulo late aperto; semicellule late subsemicirculares 
et profunde quinquelobe, incisuris inter lobos late apertis ; lobo 
polari cum lateribus subparallelis, prope apicem subito dilatato, 
apice retuso-emarginato, angulis emarginato-dentatis, cum denti- 
culo minuto intra marginem angulos emarginatos versus ; lobis 
lateralibus equalibus, in lobulis equalibus 4 divisis, incisura 
mediana multe profundiore, lobulis emarginato-dentatis; cum 
serie denticulorum minutorum intra margines incisurorum pri- 
mariarum 4 et sinus. 
Long. 142-151 p; lat. 142-147 p; lat. isthm. 18 p. 
Hab. Loch Ruar, Sutherland (J. Murray) ! 
This species was in abundance, and its characters, which are 
very constant, do not agree with those of any described species 
of Micrasterias. The incisions between the lobes and lobules are 
all widely open with concave sides, which causes them to be 
widest about the middle. The sinus, which is more open than 
that of any other incised Micrasterias, is one of the most striking 
features of the species. 
The only two species with which it could be confounded are 
M. papillifera, Bréb., and M. radiosa, Ralfs (particularly var. 
ornata, Nordst.). 
From ML. papillifera it is distinguished by the widely open 
sinus and incisions, which are also deeper, and by the very 
different form of the polar lobe. It is distinguished from 
M. radiosa by the widely open sinus and incisions, which are not 
so deep, and by the absence of the further subdivision of the 
superior lateral lobes. 
MM. Murrayi possesses a series of minute denticulations along 
the margins of the sinus and each of the incisions between the 
lobes. This character is present in WM, papillifera, and also in 
M. radiosa var. ornata. 
Var. TRIQUETRA. (PI. 15. fig. 3.) 
Var. cellulis triquetris, a vertice visis triradiatis. 
Long. 163; lat. 151 p; lat. isthm. 16 p. 
Hab. Loch Doon, Ayrshire. 
This extraordinary variety is of great interest, as only one 
ey fF 
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