74 Greville, on Neiv Diatoms. 



This beautiful genus appears to be a very natural one ; its 

 characteristic feature being the coronal circle of large cellules, 

 and the curved or spiral arrangement of the cellules within 

 the circle. The typical species, B. coronata, has never, I 

 believe, been found entire, the greater portion of the border 

 being always absent. On two occasions only have I obtained 

 a fragment in which, along with part of the corona, was a 

 portion of perfect margin. Do the coronal cells in this species 

 invariably retain their oblong character ? Examples have 

 certainly come under my notice in which they were more round 

 than oblong, but I unfortunately omitted to mark them. It 

 is, however, by no means improbable that the valves referred 

 to may belong to an undescribed species. 



Triceratium. 



Triceratium notabilis, n. sp., Grev. — Large. Valve punctate, 

 with straight sides; angles broad, much produced, dilated, 

 oblong or somewhat rhomboidal, with a conspicuous pseudo- 

 nodule ; centre convex, with radiating puncta and several 

 spines. Distance between the angles "0025'' to •0040". 

 (Figs. 2, 3.) 



Hub. Barbadoes deposit; rare. 



Of this fine diatom above a dozen examples, including 

 broken specimens, have come under my observation. It is 

 evidently related to T. coniferum, but is a much larger species, 

 and conspicuous for the very produced angles, which are equal 

 in length to the straight sides of the valve. The prevailing 

 form of the angle is rhomboidal, but it is occasionally oblong, 

 as in fig. 3. The centre of the valve is convex, and the 

 puncta radiating as in T. coniferum, a character omitted to be 

 brought out in the figure of that species in the ' Microscopical 

 Journal.^ The centre is also furnished with spines, no 

 fewer than seven being present in fig. 3, while in the specimen 

 represented at fig. 2, two are situated at the base of each 

 angle. The Barbadoes deposit has yielded me several other 

 frustules, which form a highly characteristic little group, of which 

 T. coniferum may be regarded as the type, but whether some 

 of them ought to be considered species or mere varieties is 

 extremely difiicult to say. They all agree in the radiating 

 punctation, convex centre, spines, and pseudo-nodules, but 

 difier considerably in form and relative proportions. Of these 

 diatoms figures will be given on a future occasion. 



Triceratium microcephalum, n. sp., Grev. — Valve with con- 

 vex sides and slender, produced, subcapitate angles, farnished 

 with pseudo-nodules ; entire surface, except a small, central. 



