BRIGHTWELL, ON TRICERATIUM. 275 



11. Vav. y. Frustule not only with numerous short spines, as in var. a, 

 but having numerous long and stout horns proceeding from the surface of 

 the valve. 



This last has more the aspect of a distinct species ; and if so, I propose 

 to call it T. horridum. 



Algerian deposit ? Plate XVII., fig. 12. 



12. T. marginatum, n. s. — Frustule surrounded ■with a broad margin 

 or frame, having transverse canaliculi, and two large circular cells at each 

 angle. Surface of the margin with small circular cells, and of the centre 

 with small radiated cells. 



Plate XVIL, fig. 13. 



13. T. radiatnm, n. s. — Frustule large, surface undulated and de- 

 pressed in the centre, covered with minute puncta or cellules, arranged, 

 as in T. condecorum, sides nearly straight, angles sharp, but without 

 comua or horns. Short radiated lines proceed from the centre, outwards, 

 and from each of the sides inwards. 



Ikrbadoes deposit. Plate XVIL, fig. 14, 



14. T. tahellarium, n. s. — Margin of the frustule thickly studded with 

 small cells, indented along the inner side in foliaceous curvatures ; surface 

 of the frustule sjiotted with small patches of cells. Angles with small 

 cornua or horns. 



Honduras. Plate XVIL, fig. 15. 



15. T. hyaJinum., n. s. — Small, transparent, surface with very minute 

 dots or cells, sides regular and straight, angles without spines. 



Barbadoes. Plate^XVIL, fig. 16. 



Section III. Ends of the angles entirely rounded off. 



IG. T. Marylandlcuvi, n. s. — Surface of the frustule covered with nu- 

 merous delicate finely-punctured parallel striai or lines, radiating from a 

 central pseudo nodule —a stout short sjiine placed laterally near each 

 angle, and in some frustules a spine also in the centre of each side ; sides 

 nearly straight, with the ends clean rounded off. 



Maryland deposit ; P. Bailey. 



Fragments of the frustules of this singular and beautiful species are 

 common in this deposit, but perfect ones are rare. 



Plate XVIL, fig. 17. 



17. T. punctatum, n. s. — Surface covered with large cell-like puncta, 

 suddenly diminishing in size at the rounded angles ; frustules somewhat 

 stout. This species varies much in size, and in the stoutness of the 

 puncta. 



Arctic Eegions. Plate XVIL, figs. 18 a, 18 b, 18 c. 



18. T. variable, n. s. — This species resembles T. alternans, but is larger, 

 and has not only three lines, as in that species, but an indefinite and va- 

 riable number of other lines, upon the surface of the frustule. The angles 

 also are prone to run out into bizarre and ever-varying forms, giving a 

 grotesque appearance to the frustules. 



Peruvian Guano, and in slides, from Mr. Topping, marked " Infusoria 

 Gomara." Plate XVIL, figs. 19 o, 19 b, 19 c. 



19. T. jmrmula. — Minute, frustules thickly punctate ; sides convex, 

 with small projecting papillaform angles, the outline of the frustule re- 

 sembling a little shield. 



Port Natal, South Africa. Plate XVII., fig. 2. 



20. T. orbicidatum. Shadbolt, see below, PL XVIL, fig. 20, a. h, 



