42 
GiiEviLLE^ on New Diatoms. 
CosciNouiscus. 
Coscinodiscus armatus, n. sp._, Grev. — Cellules minute, equal, 
radiating, about 13 in •001"; the disc furnished, towards the 
margin, with numerous, radiating, spine-like ridges. Diameter 
•0025" to •0035". (PL IV, fig. 5.) 
Hab. Barbadoes deposit ; very rare. 
A curious species, resembling very closely, in the marginal 
ridge-like spines or processes, Brightwellia Johnsoni (Ralfs, 
MS.); one of the most beautiful of the many new diatoms 
which have been found in this deposit. When the disc is 
viewed in the position in which it usually presents itself, that 
is, vertically, these processes appear as short, thickened lines 
tapering towards the centre ; but an oblique view brings out 
their real character. 
Coscinodiscus tuberculatas, n. sp., Grev. — Disc with a deep 
pore-like umbilicus; cellules radiating, subequal, the longer 
series terminating in marginal tubercles ; cellules 9 in •OOl"; 
marginal striae 25 in -001". Diameter '0025'' to ^0035", or more. 
(Fig. 6.) 
Hab. Barbadoes deposit ; frequent. 
Cellules hexagonal ; those immediately surrounding the um- 
bilicus small ; the rest nearly equal till near the margin, where 
they become again smaller. The longer rays of cellules appear 
to be in pairs, and it is the line of separation between them 
which terminates in the tubercle. The latter, on an oblique 
view, is seen to form an obtuse process. The margin is dis- 
tinctly and rather broadly striated. 
Coscinodiscus biradiatus, n. sp., Grev. — Granules distinct, 
filling up the centre irregularly, afterwards radiating, large, 
prominent, somewhat quadrangular, gradually diminishing 
in size to the margin ; rays distant, the long ones alternating 
with a shorter series ; margin with a row of minute puncta. 
Diameter •0035". (Fig. 7.) 
Hab. Barbadoes deposit ; rare. 
An object of exceeding beauty and brilliancy. The disc 
is very convex ; and in taking a vertical view, and in passing 
the focus down the side of the disc, the efiect is very 
striking ; the prominence of the granules being so great as to 
cause the rays, when so viewed in perspective, to resemble 
the ribs and tubercles of a Cardium. There is no umbilicus. 
Coscinodiscus elegantuluSy n. sp., Grev. — Granules minute, 
subequal, irregularly scattered over a central space equal to 
about a third of the diameter of the disc ; they afterwards 
form a single series of distant, often somewhat curved, rays ; 
margin with a row of very minute puncta. Diameter •OOl^". 
(Fig. ?.) 
