13 
Descriptions of New and Rare Diatoms. Series VIII. 
By R. K. Greville, LL.D., F.R.S.E., &c. 
(Communicated by E. C. S. Roper, E.R.S.) 
Plagiogramma. 
Plagiogramma Robertsianum, n. sp.^ Grev. — Valve lanceo- 
late, obtuse ; costse 2, centrical ; striae very fine, about 30 in 
•001". Length -0018" to -0030". (PL I, figs. 1, 2.) 
Hab. Port Stephen, New South Wales ; Dr. Roberts. 
Unquestionably distinct, with finer striae than in any 
species previously described. Indeed, under a moderately 
magnifying power, they are invisible. The frustules vary, to 
some extent, in shape and size ; the more minute examples 
being somewhat elliptical, the larger ones narrower in pro- 
portion to their length, and, generally, slightly constricted 
below the apices, where a few very minute, raised points are 
situated. These come out most distinctly in the front view, 
but even then require careful adjustment. 
Campylodiscus. 
Campy lo discus ornatuSj n. sp., Grev. — Valve nearly circular, 
much bent, with two bands of radiating canaliculi, the mar- 
ginal one narrow, the inner one much broader, the canaliculi 
distant, with two rows of puncta between them ; central space 
filled with faint, obscurely moniliform, radiating lines, and bor- 
dered with a row of oblong granules. Diameter '0056''. (Fig. 3.) 
Hab. On Tridacna, West Indies ; F. Kitton, Esq. 
An exquisitely beautiful diatom, having some relation to 
Campylodiscus Horologium, in its circular form, distant cana- 
liculi, and intercanalicular puncta ; but differing from it in 
the much-bent valve and in the double band of canaliculi, 
besides various minor points. In the inner band, which is 
about twice the breadth of the outer one, the long canaliculi 
alternate withvery short, imperfect ones, while in the outer band 
they are all equal, and correspond in number with the perfect 
and imperfect canaliculi, taken together, of the inner band. 
Campylodiscus Wallichianus, n. sp., Grev. — Valve circular, 
with a defined, broadly linear, central space ; canaliculi about 
48, concentric, with extremities very slender, and armed with 
minute spines. Diameter -0040". (Fig. 4.) 
Hab. Dredged off St. Helena by Dr. Wallich, in from 
fifteen to forty fathoms. Harvey Bay, Queensland, and Port 
of France, New Caledonia, Dr. Roberts. 
