'KEPOKT ON THE JDIATOMACE^E. HI 



Triceratium abyssale, n. sp. (Plato XIII. fig. 6.) 



Forma orbiculato-triangularis, apicibus late rotundatis, in ocellum exeuntibus ; 

 lateribus convexis ; valva punctulis aequalibus radiantcr siguata. In mari Indico. 



This form possesses large rounded extremities and convex sides, so that the frustule 

 becomes suborbicular. The valve has equal radiating lines of punctations slightly con- 

 ver° r in° r at the obtuse apices, each of which terminates in a large ocellus. The specimen 

 was obtained at a depth of 2050 fathoms. 



Triceratium insutum, n. sp. (Plate XXV. fig. 7.) 



E rnaximis ; valvis novem-angulatis, areolatis ; lateribus concavis ; arcolis hexagonali- 

 bus, grandiusculis, inasqualibus ; valva exterius areolata, inferius arctissime et radianter 

 striolata. In mari Philippinarum. 



This species possesses nine angular points, and between each adjoining pair a concave 

 margin. The surface is covered by very large subhexagonal areolae, which gradually 

 diminish in size from the centre towards the periphery. The valve exhibits fine radiating 

 striae, and the areolae present at the bottom irregularly rounded spaces, which bear one or 

 more distinct and irregularly disposed granules or points. It appears certain that these 

 two kinds of ornamentation belong to two distinct strata of the diatomaceous cell wall, 

 which may sometimes become detached from one another. I became convinced of this 

 when Dr James Rae, E.N., drew my attention to a Triceratium in which only a part 

 of the inner striated layer still adhered to the valve. A similar doubly laminated wall 

 may be seen in Triceratium favus, Ehrenb., and in Triceratium grunoivianum above 

 referred to ; but the nine-angled frustule now in question cannot be united with these, 

 not only because of the little points in the centre of the areoles, but still more because 

 of the absence of the raised terminal processes which are presented by the others. 



In consequence of this bilamination of the frustular wall, it becomes necessary to 

 exercise great caution in the establishment of new species of this genus. 



Triceratium atlanticum, n. sp. (Plate XVII. fig. 3.) 



Forma quadrato-globosa, cellulis grandiusculis a quinque majoribus mediis radiantibus, 

 et leviter ad quatuor ocellos terminales convergentibus. In Oceano Atlantico ad insulas 

 Azores. 



This specimen possesses four very obtuse angles, between each of which the sides 

 are convex, so that the resulting form is suborbicular. The cellules are of somewhat large 

 size, and radiate from a small central rosette formed of five large cellules. Each of the 

 angles presents an elliptical ocellus, and towards each of the four extremities the cellules 

 become slightly convergent. 



