GiiEviLLE^ on New Diatoms. 
9 
Hab. Barbadoes deposit^ Cambridge estate ; in slides 
communicated by C. Johnson, Esq. 
A most brilliant and beautiful diatom allied to T. lobatum, 
but apparently distinct. The arms are much longer and 
narrower ; and the punctation is confined to the intervals 
between the lines on the same side, thus leaving a well-defined, 
broad, blank space extending down the middle of each arm to 
the central area. The latter is occupied by a small cluster 
of puncta opposite each side-angle, with a few scattered inter- 
mediate ones, so as to enclose an obtusely triangular blank 
space. Distance between the arms -0028'^ 
Triceratium cancellatum, n. sp., Grev. — Valve with slightly 
concave sides and subacute angles ; surface with 6 alternate 
radiating elevations and depressions, filled with radiating 
lines of cellules which become large and somewhat quadrate 
towards the margin and angles, which latter contain large 
pseudo-nodules. (Fig. 17.) 
Hab. Barbadoes deposit, Cambridge estate; C. Johnson, 
Esq. ; extremely rare. 
A very curious and unquestionably distinct species. The 
surface is undulated in such a way that when the angles are 
in focus, they appear to terminate a ridge or elevation which 
radiates from the centre, while the middle of the margin at 
each side is out of focus, and in like manner terminates a 
radiating depression. The cellulation gradually increases in 
size from the centre to the margin, and to the angles, where 
it ends abruptly at the pseudo-nodules which, in the front 
view must be considerably elongated processes. There is a 
sort of indication of the commencement of vein-like lines, 
here and tliere at the margin, especially near the angles, which 
is shown by some of the cellule-walls becoming thickened for a 
short distance inwards. Distance between the angles '0032^'. 
Triceratiim acceptum, n. sp., Grev. — Small ; valve with 
nearly straight sides and obtuse angles containing a conspi- 
cuous roundish pseudo-nodule ; structure composed of lines 
of minute puncta radiating from an umbilicus of a few larger 
puncta, the lines diverging in a fan -like manner to the sides, 
and converging towards the angles. (Fig. 21.) 
Hab. Barbadoes deposit, Cambridge estate; in slides 
communicated by C. Johnson, Esq. 
Although the sides of the valve are nearly straight, there 
is a perceptible approach towards convexity. The pseudo- 
nodules are transversely roundish-oval, and somewhat re- 
semble the mastoid process of an AuUscus. Distance between 
the angles •0025"". 
Triceratium exornatum, n. sp., Grev. — Rather large ; valve 
VOL. XIII. b 
