Greville, on New Diatoms. 83 



One of the most beautiful diatoms known, and closely 

 allied to the preceding. In this case the radiating lines of 

 the centre are genniue costse, each of which, as it terminates 

 at the margin of the inner triangle, becomes capitate, pro- 

 ducing an exquisitely ornamental effect. The pseudo- nodules 

 are large, flat, and oblong ; and an approach is made to the 

 double pseudo-nodule of the preceding species, by their 

 being traversed by two fine oblique lines, which, meet at the 

 apices of the angles of the inner triangle ; and what brings 

 the approach still closer, is the fact that it is the division 

 next the angle of the valve only which is punctate. A re- 

 markable peculiarity consists in the pseudo-nodules not being 

 situated in the extreme angle, as in the other species of the 

 group, but leaving space for the lateral costse to be visibly 

 continued round them. These costae are widely separated 

 throughout the greater length of the border, but increase 

 rapidly in number as they turn round the angle, so that 

 there are about twenty on each side. The angles of the 

 inner triangle are lengthened out until they enter the punc- 

 tate portion of the pseudo-nodule, and terminate in a short 

 spine. In this and the preceding species the puncta in the 

 lateral compartments are rather widely scattered. 



Triceratium Abercrombieanum, n. sp., Grev. — Valve with 

 nearly straight sides, obtuse angles, and striated margin; 

 centre a blank triangular space ; border divided by transverse 

 costse into punctated compartments ; a short line from each 

 angle of the central triangle terminating in a wide fork with 

 incurved apices, a faint, undulating line passing along the 

 middle of each border. Distance between the angles, about 

 •0023". (Figs. 7—9.) 



Hab. Barbadoes deposit, C. Johnson, Esq., Dr. Greviile; 

 extremely rare. 



At a hasty glance this might readily pass for a variety of 

 the preceding species ; but the presence of a striated margin, 

 and the totally diflerent centre, immediately dispel the 

 impression. The pseudo-nodule, besides, is single; and 

 although in one instance (fig. 9) the fork of the apex of the 

 short line terminating the angles of the central triangle forms 

 an enclosed, roundish space, instead of remaining open, it is 

 unconnected with the pseudo-nodule, and contains puncta. 

 A remarkable character in this species is a faint undulating 

 line which passes along the middle of the border, commencing 

 at the outer angle of the fork above mentioned, and ending 

 at the corresponding point in the opposite angle of the valve. 

 This line, which, although faint, may be traced without any 

 difficulty, I have found uniformly present in the four specimens 



