A FOSSIL MARINE DIATOMACE0U3 DEPOSIT. 65 



The occurrence in this deposit of the genera Craspedoporus, 

 Actinodiscus, Porodiscus, and other species, hitherto observed 

 only in the deposit from Cambridge Estate Barbadoes is an im- 

 portant fact in relation to the distribution of the Marine 

 Diatomaceas during the Tertiary period. 



Anthodiscus, n. gen., Gr. and St. — Characteristics : Valves 

 discoid, divided into numerous compartments by depressed, 

 radial, clear spaces extending from the margin, but not reaching 

 the centre. Differs from Cosmiodiscus in the fact that the radial 

 divisions are not merely clear superficial spaces, formed by the 

 absence of cellules or granules ; but are actual divisions of the 

 nature of internal septa. 



A.floreatus,n. sp., Gr. and St.— Valve circular, -0028" to '003" 

 in diam., with numerous marginal compartments (14 to 21 have 

 been observed), resembling the petals of a flower. The com- 

 partments are granular, slightly elevated at the margin, and 

 extend inwards for a length of about one -third of the radius. 



In the outer edge of each compartment is a depression or 

 notch, giving a crenulated appearance to the circumference of 

 the disc. The central portion of the disc, which is flat, has a 

 clear umbilicus, round which is a zone of granules divided irre- 

 gularly by clear rays. 



At the outside of the granular zone is a slightly depressed 

 annular clear space, from which spring the granulose compart- 

 ments or florets. 



In frustular view this form is cylindrical, with flat top, and 

 corrugated or crenulated exterior. (PI. VI., Fig 20.) 



Cosmiodiscus Normanianus, Grev. ("T.M. S.," Vol. xiv, p. 80, 

 PI. 8, Fig. 11). — We do not at present remove this form from 

 the Genus in which Greville has placed it ; though in the char- 

 acter of the radial clear spaces, it differs materially from the 

 other two species described and figured in the same place. 

 Eventually it may have to be placed in the last Genus (Antho- 

 discus), or in one of its own. It is not of very rare occurrence, 

 though usually small. We figure the finest specimen which 

 has occurred to us, and for which we are indebted to Lawrence 

 Hardman, Esq. Diam., -0022". Number of compartments, 17. 

 (PI. VI., Fig. 21.) 



It will be seen that at the marginal end of each of the clear 

 radial dividing spaces, there is a single detached punctum not 



