108 THE VOYAGE OF H.M.S. CHALLENGER. 



assume the appearance of minute points, forming very delicate striae. The walls, however, 

 are slightly concave, the general valval granulation larger, while at the centre the granules 

 are few and small, so that the genus established by Brightwell cannot be so far extended 

 as to embrace this form, which must therefore become the type of a new species.] 



Triceratium pavimentosum, n. sp. (PI. XIII. fig. 8.) 



Quadratim areolatum ; lateribus concavis ; apicibus cuneato-rotundatis ; areolis sub- 

 hexagonalibus ; apicum processu nullo. Ad mare Japonicum. 



This frustule possesses concave walls and valves ornamented with subhexagonal 

 cellules or areolae. It may be distinguished from the allied Triceratium favus of Ehren- 

 berg 1 principally by the absence at each extremity of the horn-like processes, which 

 are characteristic of the latter. Triceratium favus also possesses rectilinear or slightly 

 concave sides. 



Triceratium cariosum, n. sp. (Plate VI. fig. 6.) 



Valvis trigonis, cellulosis ; lateribus subconvexis ; apicibus rotund atis ; cellulis sequali- 

 bus nullo certo ordine dispositis et vacuis lineolis irregulariter divisis. In mari Pacifico. 



This singular Diatom possesses a triangular form, with slightly convex walls and 

 rounded extremities. The cellules that ornament the valve are equal, but have no definite 

 arrangement, although a tendency to form excentric curves may be recognised at some 

 places. Lacunae occur at irregular intervals amongst the granules, and give the valve an 

 eroded appearance. 



Triceratium punctigerum, n. sp. (PI. XIII. fig. 4.) 



Parvum, triangulare ; apicibus rotundatis ; lateribus subconcavis ; denticulo vel 

 punctulo erectiore marginali ad apices ; valvis inordinate punctulatis. In mari Pacifico. 



This small but elegant triangular Diatom was discovered in a sounding made 

 in the Pacific Ocean. It possesses rounded extremities and slightly concave sides. The 

 valve is very delicately punctated, the puuctations assuming no definite arrangement, and 

 at the margin of each extremity a more prominent granule or point may be recognised. 



Triceratium coronatum, n. sp. (Plate VI. fig. 7.) 



E maximis ; triangulare, areolatum ; lateribus convexis ; apicibus elongatis, subulatis ; 



areolis sequalibus, hexagonis granulo erecto ad quemque angulum; corona marginali 



erecta. Ad Zebu in mari Philippinarum. 



1 Ehrenberg, Kreideth., p. 79, N. 58, pL iv. fig. 10; Mikrogeol., pi. xix. p. 17; Smith, Synop. Brit. Diat., 

 voL i. p. 26, pi. v. fig. 44, and Suppl., pi. xxx. ; Heiberg, Conspec, p. 41 ; Jan. et Rabenh., Hondur., p. 14, 

 pi. iii. fig. 10; =(1.) Triceratium megastomum, Brightwell, Micr. Joum., voL i. ; (2.) Triceratum fimbriatum, 

 Wallich, Micr. Joum., voL vi. p. 247, pi. xii. figs. 4-9. 



