104 
Greville_, on New Diatoms. 
The margin is strong, narrow^ and destitute of puncta as it 
passes rouad the angles. 
Triceratium reticulatum, n. sp., Grev. — Yalve 6-lobed_, with 
a narrow, striated margin ; lobes or angles broadly rounded ; 
surface filled with a large reticulate cellulation, radiating in 
fasciculi towards the spaces between the angles, and becom- 
ing smaller towards the circumference. Distance between 
the angles -0019'^ (Fig. 21.) 
Hab. Barbadoes deposit, Cambridge estate ; in slides com- 
municated by C. Johnson, Esq. Extremely rare. 
An exquisitely beautiful species. Cellules subquadrate^ 
radiating from a single cellule in the ceutre. 
Triceratium quadratwnj n. sp., Grev.— Large; valve with 
4 subobtuse angles and straight sides, from each of which 
project inwardly 4 — 5 short vein-like lines ; surface filled with 
roundish subequal cellules, scattered in the centre, but soon 
radiating ; angles with roundish pseudo-nodules. Distance 
between the angles -0050'^ (Fig. 19.) 
Hab. Barbadoes deposit, Cambridge estate ; C. Johnson, 
Esq. 
All the specimens I have seen of this fine diatom are 
4-angled. In the centre there is often a sort of umbilicus, 
or, at least, a somewhat irregular circle of smaller cellules, 
around which the ordinary cellules are often more or less 
scattered before they pass into radiating lines, in which they 
are 4 — 5 in •001"". Generally, if not always, a few short 
central spines are present. 
Triceratium par allelum (Ehr.), Grev. — Small; valve 4 — 6- 
angled; angles slightly rounded, the sides straight; centre 
widely and ftiiutly reticulate, while a broad band of parallel, 
subremote lines of granules fills up the space between the re- 
ticulation and the narrow margin. Distance between the 
angles -0018.^' (Figs. 22 and 23.) 
Amphitetras parallela, Ehr., 'Leb. Kreideth.,^ p. 63, fid. 
Kutz.; Kiitz., ^Bacill.,^ p. 135; ^ Sp. Alg.,^ p. 134; Ralfs, 
inPritch. ^nf.' (1861), p. 858; Rabenh., ^ Fl. Eur. Alg.,' 
p. 318. 
Hab. Greece (fossil) ; Moron deposit (fossil) ; Red Sea 
dredgings, L. Hardman, Esq. 
The present diatom satisfactorily illustrates the transition 
from a four- to a six- angled valve. Both forms occur in 
slides prepared by Mr. Hardman from. Red Sea dredgings, 
and it is impossible to deny their specific identity. The 
triangular valve, however, has not been observed. The 
quadrangular form being alone known to Ehrenberg, led him 
probably to refer it to the genus Amphitetras ; but after our 
