Greville, on New Diatoms. 71 



most remarkable. About half a dozen examples have been, 

 observed. The interval between the margin and the central 

 labyrinth of lines is blank, with the exception of a few short, 

 vein-like lines given off from the central network, some of 

 Avhich nearly reach the margin. In this, as in many other in- 

 stances, a figure will convey a better idea of the object than 

 the most elaborate description. 



Triceratium areolatum, n. sp., Grev. — Valve with slightly 

 concave sides and acute angles ; surface covered with rather 

 large, circular areolae, Avhile very short, vein-like lines project 

 from the sides of the valve. Distance between the angles 

 •0026". (Fig. 13.) 



Hab. Barbadoes deposit ; extremely rare. 



I do not know any member of the genus with which this 

 diatom can be compared, unless it be T. acutum, Ehr., with 

 which it agrees in the rather peculiar areolation. From that 

 species, however, it differs in the sides of the valve being 

 decidedly, although slightly, concave, and in the angles not 

 being in the smallest degree elongated. The short, vein-like 

 lines present, in addition, a conspicuous differential cha- 

 racter. Nevertheless, I am not certain of its being distinct. 



Triceratium tesseUatum, n. sp., Grev. — Valve with straight 

 sides and rounded angles, somewhat convex in the centre; 

 surface filled with subquadrate, large, more or less concentric 

 granules, becoming smaller at the angles ; margin with a row 

 of minute granules, 11 in 'OOl". Distance between the angles 

 •0025". (Fig. 14.) 



Hab. Deposit on the banks of Pertuxent River, near Not- 

 tingham, Maryland, United States. 



Distinguished by the large size and more or less square 

 form of the granules, especially those of the convex centre. 

 Smaller granules completely fill up the angles. In some ex- 

 amples the convexity of the centre is scarcely at all apparent. 



Triceratium robustum, n. sp., Grev. — Valve with straight 

 or very slightly concave sides and rounded angles with 

 pseudo -nodules; surface filled with irregularly shaped, coarse 

 ■ granules, those in the circumference of the convex centre and 

 at the angles small, the rest large. Distance between the 

 angles -0030" to -0040'. (Fig. 15.) 



Hab. Cove, Calvert County, Maryland, United States. 



A strong, coarse-looking species, with a large, clear, pseudo- 

 nodular space at the angles. The granules are very irregular, 

 small ones being often mixed with the large ones. Some- 

 times a concentric arrangement is conspicuous, but in other 

 cases it is very partial, being most distinct between the con- 

 vex centre and the angles, where also the largest granules 



