208 GREVILLE, ON PLAGIOGRAMMA. 
PLAGIOGRAMMA, Grev. 
Frustules quadrangular, direct, two or more united into a 
filament; valves linear or elliptical; strize moniliform ; vitte 
two or more, pervious, parallel with the strie. 
Section I.—Vittz 2, centrical. 
1. P. gregorianum, Grev.—Valve elliptical, obtuse ; strize 
pervious, 18 in ‘001; frustule in front view somewhat dilated 
in the middle; length -0014” to :0030."” (Pl. X, figs. 1, 2.) 
Denticula staurophora, Greg., ‘'Trans. Roy. Soc. Ed.,’ vol. 
xxl, p. 496, pl. x, fig. 37. 
Dredged in Loch Fine, by Dr. Gregory. LLamlash Bay, 
Island of Arran. 
This was justly regarded by the late Professor Gregory as 
a very curious little diatom, nothing similar to it having been 
previously noticed. As far as I have had an opportunity of 
examining the side views of the different species, this is the 
only one which possesses pervious strie. It is scarcely 
necessary to remark that, as the centrical vitte which 
Dr. Gregory regarded as a stauros, are characteristic of all 
the species, I have been under the necessity of changing the 
specific name. 
2. P. gamaicense, nu. sp., Grev.— Valve ..... ? frustule 
in front view with the sides straight; length 0024”; striz 
continued almost quite up to the angle, 16 in ‘001. (Fig. 3.) 
Jamaica, in washings of alge. 
As I have not succeeded in obtaining a side view of the 
frustule, I am unable to give a satisfactory definition of this 
species. The vitte, however, are only centrical, and it is 
certainly distinct from the preceding. The strize can scarcely 
be termed strictly moniliform, but rather moniliform costate. 
I have another form belonging to this section, also from 
Jamaica, the frustules of which are ‘0020" in length, and the 
band of striz considerably narrower; the striz themselves 
21 in 001". It may be a different species, but having only 
seen the front view, I dare not venture to introduce it as 
such. 
3. P.? tessellatum, n. sp., Grev.—Valve narrow-elliptical ; 
with parasites and entangled with zoopbytes, forming what the mere col- 
lector of algee would call unsightly tufts. They must on no account be washed, 
but dried in the rough, just as picked up, and then packed in coarse paper. 
Small parcels of this kind (a few ounces in weight), from the coasts of the 
different islands (and from different localities of the same island), could not 
fail to produce objects of the highest interest to the diatomist. 
