NAVICULA ABRUPTA. 13 
band linear, narrower towards the apices; unstriated 
area bilunate. 
Hab. Marine. Lamlash Bay Isle of Arran and Loch 
Fyne (Prof. Gregory). 
Navicula abrupta, Gregory. 
Nivicula Lyra, var. abrupta, Greg. Diat. of the Clyde, p. 14, pl. i. fig. 14 ; 
Rabenh. Europ. Diat. p. 178. 
Navicula lyra, Sm. Synop. vol. ii. p. 93, pl. xvii. fig. 152a*. 
Plate II. fig. 6. 
V. elongated, oval; strie grannular, about 24 in -001"; 
marginal band broad in the middle, tapering towards 
the extremities, with a bicrescentic inner border, 
median band with a convex outer border; unstriated 
area narrow, incurved in the middle and at the extre- 
mities; dry valve colourless. 
In some specimens the extremities of the unstriated 
longitudinal area reach near to the apices of the valve, in 
others they terminate abruptly some distance from them ; 
in this respect considerable variation is observed. 
I have, without hesitation, separated this form from N. 
Lyra, Ehren., with which it has been confounded, but from 
which it is essentially different ; it never occurs with pro- 
duced extremities, and the longitudinal unstriated area is 
always incurved towards its extremities, not everted as in 
N. Lyra. 
Hab. Marine. Lamlash Bay Isle of Arran (Prof. Gre- 
gory); Poole Bay (Prof. Smith); Estuary of the river 
Coquet, Northumberland, plentiful (A. S. D.). 
