GREVILLE; ON NEW DIATOMS. 335 



prominent granules, each planted within a little square com- 

 partment ; so that when the valve is focussecl to bring these 

 spaces or compartments into view, nothing is seen but a 

 simple clathrate structure, in which it differs from Odon- 

 ticlium, Diadesmis, and other genera, with which, in one 

 aspect or another, it may be compared. In the front view 

 are seen double longitudinal rows of minute dots, as in 

 Playioyramma ornatum, and as the period of division ap- 

 proaches additional rows make their appearance. 

 Glyphodesmis eximia, n. sp., Grev. (Figs. 7 — 10.) 

 Hab. In scrapings of conch shells from Nassau, New 

 Providence (communicated bv Mr. G. Norman), Jamaica; 

 E. K. G. Dredgings off St. Helena, in from fifteen to forty 

 fathoms; Dr. Wallich. 



The lateral view of this beautiful diatom is obtusely ellip- 

 tical; the central nodule very large and urabonate; the 

 median line generally expanding somewhat as it approaches 

 the nodule, while a small, vacant space surrounds the latter, 

 as in many Navicidce and Pinmdaria. The transverse moni- 

 liform strise are robust and equal, the number of granules 

 composing them being not more than three or four in the 

 widest part of the valve. The clathrate structure is very 

 similar to the quadrangular cellulation observed near the 

 margin of Triceratium margaritacewn and its allies, and the 

 granules are also very similar to those of that diatom, only 

 relatively larger and more compactly arranged. At each ex- 

 tremity of the frustule is a small vacant space, caused by the 

 abrupt termination of the transverse striae. Like most dia- 

 toms whose frustules are disposed in filaments, the present one 

 varies greatly in point of size, being occasionally both smaller 

 and considerabh^ larger in length and breadth than any of 

 the frustules I have represented. The ordinary dimensions^ 

 however, may be said to be intermediate between figs. 6 

 and 7. It is very satisfactory to find that my drawings of 

 this species from West Indian specimens are confirmed by 

 careful sketches made by Dr. Wallich from those dredged by 

 him at St. Helena, and kindly placed in my hands. 



Mastogloia. 



Mastogloia capitata, n. sp., Grev. — Valve elliptic oblong 

 with produced, distinctly capitate apices^ and 7 — 11 (rarely 

 more than 8 or 9) loculi; strise very obscure. Length aboui 

 •0015". (Figs. 11, 12.) 



Hab. Fresh-water tank, near Calcutta; Dr. Macrae. 



Mastogloia Smithii, var. /3, which has produced and inflated 



