ROPER, ON BRITISH MARINE DIATOMACES. 23 
I have met with a few specimens of the same form in a 
gathering of M. De Brébisson’s, containing Nitzschia palpe- 
bralis, &c., from Normandy, kindly sent me by Professor Smith. 
Actinocyclus triradiatus, nu. s.—Valve with three rays, the 
surface covered with minute puncta or dots, with faint lines 
connecting them ; the rays formed by slight elevations, with 
a more closely dotted structure. Diameter -003" to ‘004 (fig. 
5 a and 0). 
Brackish water. Near Caermarthen. 
This species occurs occasionally in clay, obtamed by my 
friend, Mr. Okeden, from a brick-yard near Caermarthen, de- 
posited probably by the tidal estuary that runs up to that 
town. The general structure of the valve differs from all the 
described species of this genus, having no distinct margins to 
the segments, or any pseudo-nodule in the centre of the valve. 
I consider, however, that it must be referred to Actinocyclus 
without hesitation, and should have adopted Ehrenberg’s 
name of Ternarius, but, from the figure in the ‘Microgeologie,’ 
that species appears to have distinct cells, and the rays are 
similar to those in A. undulatus, and not elevations, or pro- 
bably thickened cell-walls, as in this species. The peculiar 
arrangement of the dots is shown in the enlarged fig. 5 6. 
Nitzschia virgata, n. s—F. V. quadrangular, linear; S.V. 
hnear-lanceolate, slightly arcuate, with produced and rather 
obtuse extremities; striz distinct, dilated at intervals into 
prominent ridges on the inner margin. Length :00405” to 
70053"; strie 26 in 001”. (Fig. 6: a, side view; 0, front 
view.) 
Marine. Dredged off Tenby, Rev. J. Guillemard. 
The outline of this species differs but slightly from that of 
Nitzschia amphioxys, w.s.; but that is decidedly a fresh-water 
species ; its extremities are more acutely lanceolate, and the 
valve more arcuate ; the striz also terminate in puncta or 
dots, stead of dilating into distinct bands, asin this species, 
which was dredged in five fathoms, at about five miles from 
the shore, and may be considered purely marine. The strongly 
curved inner margin, and slightly recurved obtuse extremities, 
as well as the peculiar thickened striz, separate it from 
N. vivax. 
The dark bands appear to arise from a thickening of the 
strie at irregular intervals, varying from the third to the 
first in succession, and extend on an average about one third 
of the breadth of the valve, being shorter at the centre 
VOL. VI. D 
