Boyal Microscopical Society. 205 



II. — A Description of some New Species of Biatomacese. 



By F. KiTTON, Norwich. 



(Bead before the 1"!oyal Microscopical Society, Oct. 1, 1873.) 



Plate XXXVIII. 



The genus Aulacodiscus is perhaps of all genera of Diatomaceae the 

 richest in beautiful forms, as the drawings by the late Dr. Greville, 

 which have so often adorned the pages of the ' Transactions of the 

 Eoyal Microscopical Society,' can testify. 



A large proportion of these Diatomaceous gems were obtained 

 from the Barbadoes deposits, and the species I have now the honour 

 of describing was also procured from the same source. Unfortu- 

 nately the quantity sent was almost infinitesimal, and yielded only 

 two valves. The precise locality from whence this material was 

 obtained is Clark's Cliff, Barbadoes. 



Aulacodiscus superhus, n. sp., F. K.— Valve with a large central 

 heptagonal depression, processes placed on the margins of the seven 

 cuneate inflations. The heptagonal area marked with large hemi- 

 spherical elevations, less conspicuous on the remainder of the valve, 

 the surface of which (with the exception of a small central smooth 

 space) is covered with distinct radiant moniliform striae ; striae about 

 18 in 'OOl"; diameter of valve, "0050"; length of sides of 

 heptagon, -0033". Fig. 1. 



Clark's Cliff, Barbadoes. 



I am indebted to my friend A. Cole, Esq., of Liverpool, for the 

 opportunity of figuring and describing this very beautiful form, who, 

 risking the tender mercies of the Post Ofiice smashers, kindly sent 

 his specimen for my inspection. Under a f objective the mulberry- 

 like prominences are very distinct on the heptagonal area, but are 

 less conspicuous as they approach the margin. The puncta are 

 distinctly radiant from the centre to the circumference. 



Sticiodiscus Crozierii, n. sp., F. K. — Valve with numerous irre- 

 gularly undulating cost«, which become very delicate as they ap- 

 proach the centre, within a short distance of the margin they 

 divide, the spaces between the costae distinctly punctate, central 



DESCEIPTION OF PLATE XXXVIII. 



Fig. 1. — Aulacodiscus superhus x 500. 

 ,, 2. — Sticiodiscus Crozierii x 400. 

 „ 3. — Isthmia vitrea (frustules) x 400. 



a, Ditto, ends of two frustules, dividing — 

 „ 4. — a. Hexagonal cells of /. nervosa x 600. 



h, „ „ „ X 1500. 



,, 5, — Nitzschia ventricosa, a. f. v. X 400. 

 „ 6. — „ decora x 400. 

 ,, 7. — TrijUioncUa co7ispicua x 400. 



