TRANSACTIONS OF THE MICROSCOPICAL 
SOCIETY OF LONDON, 
7 
Descriptions of New and Rare Diatoms. Series XXo 
By R. K. Greville, LL.D., F.R.S.E., &c. 
(Communicated bj P. C. S. Roper, F.L.S. &cO 
(Read May 9th, 1866.) 
(Plates XI and XII.) 
Plagiogramma. 
Plagiogramma elongatum, n. sp._, Grev. — Frustules elon- 
gated_, with two central costse ; valve linear^ narrower towards 
the rounded apices_, generally very slightly contracted in the 
middle ; strise composed of rows of large^ distinct,, subquad- 
rate grannies. Length -0074^^ (PI. XI, figs. 1, 2.) 
Hab. In cleanings of shells from South America; Laurence 
Hardman, Esq. 
In the character of the markings this noble species 
is allied to P. tessellatum, but^ it is twice the size, and the 
valve is of a different form, linear instead of elliptical, rounded 
at the ends, near which it becomes narrower and more strictly 
linear. It is the finest species of the genus hitherto dis- 
covered. 
Plagiogramma? angulatum, n. sp., Grev. — Frustule in front 
view linear, with parallel sides, central and terminal costse ; 
the space between the terminal costse and the apex oblique ; 
strise forming a very narrow band, ^0 
Hab. Barbadoes deposit, Cambridge estate ; in slides com- 
municated by C. Johnson, Esq. ; extremely rare. 
All the specimens I have met with present the front view ; 
and as the ends are distinguished from those of all the other 
species in being, as it were, sharply bevelled off on each side, 
some slight doubt may exist as to its generic position. The 
VOL. XIV. I 
