97 
Descriptions o/New and Rare Diatoms. Series XVII. 
By R. K. Greville, LL.D., F.R.S.E., &c. 
(Communicated E. C. S. Ropeu, F.L.S., &c.) 
(Read June U, 1865.) 
Piates VIII & IX. 
Cladogramma. 
Frustules simple^ disciform; lateral valves convex, marked 
with radiating, irregularly forked lines; connecting zone 
ring-like. 
I am not aware that Ehrenberg has anywhere defined this 
genus, which is only known by the figure he has given of his 
Cladogramma Californicum Microgeologie/ pi. 33, 13, 
f. l"^"^). Ralfs, in introducing it into his arrangement, in 
Pritchard^s ''History of Infusoria' (1861), gives a copy of the 
figure above referred to, but also adds, The characters of 
this genus are unknown to us.'^ Under these circumstances, 
I have, in adopting Ehrenberg^s name, ventured to supply a 
generic character. 
Cladogramma conicum, n. sp., Grev. — Lateral valves coni- 
cal, with numerous, nearly straight, forked, or simple lines. 
Diameter '0017'^ (Figs. 1 and 2.) 
Hab. Barbadoes deposit, Cambridge estate; in slides com- 
municated by C. Johnson, Esq ; rare. 
It is quite possible that the present diatom may difi^er from 
Ehrenberg's undefined genns, of which only the hemispheri- 
cal valve has been discovered. Mr. Kitton obtained a single 
specimen, which was unfortunately lost in its transit through 
the post-office, and with it the opportunity of determining 
the question. His sketch, now before me, is precisely simi- 
lar to Ehrenberg's figure, showing about four lines radiating 
from the centre, which divide and subdivide into diverging 
branches, about half way between the centre and margin. 
In the present species the valve is distinctly conical, and the 
lines radiate rather closely from the very centre, dividing in 
a straight manner somewhat irregularly, with occasional in- 
dependent lines, to fill up the spaces, so that at the margin 
all the lines are nearly equidistant. The connecting zone ap- 
pears to be slightly vertically rugose. 
Thaumatonema. 
TJiaumatonema ? cos latum, n. sp., Grev. — Minute ; disc 
