43 Greville, on New Diatoms. 



COSCINODISCUS. 



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". (PI. 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 tuberculatus , n. sp., Grev. — Disc with a deep 

 pore-like umbilicus; cellules radiating, subequal, the longer 

 series terminating in marginal tubercles ; cellules 9 in "001"; 

 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 •OOSS". (Fig. 7.) 



Hab. Barbadoes deposit ; rare. 



An object of exceeding beauty and brilliancy. The disc 

 is very convex ; and in taking a vertical -sdew, and in passing 

 the focus down the side of the disc, the effect 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 elegantulus, 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 '0017". 



(Fig. y.) 



