28 
GrevillEj on New Diatoms. 
of the whole group being generally areolate or punctate. 
The cellules are 7 in -001'^ Breadth of frustule '0030". The 
horns appear to be short, but in H. Polycystinorum this is a 
variable character. The central projection forms a gentle 
arch and there is a slight one on each side, but if we are to 
judge from the species above named, this also is sometimes 
an equally variable character. 
Hemiauius mucronatus , n. sp., Grev. — Rectangular; angles 
produced into rather short horns tipped with a spine at the 
inner angle; space between the horns nearly straight, with 
a large, central, convexo-conical projection, bearing a minute 
mucro on its summit ; structure composed of equal, roundish, 
quadrate cellules arranged in parallel lines. (Fig. 6.) 
Hab. Barbadoes deposit, Cambridge estate ; in slides com- 
municated by C. Johnson, Esq. 
Of this species I have seen many examples ; and as it has 
much of the general appearance of H. Polycystinorum, I 
have no doubt that I have frequently passed it over for that 
diatom. The eye requires to be specially directed to the 
cellulation which of itself is a sufficient diagnosis. Looking 
at the valve in its front view, as represented in the figure, 
the cellules form vertical parallel lines. They are 5 in 'OOl''. 
Breadth of frustule '0030^^ 
Hemiauius punctatus, n. sp., Grev. — Rectangular ; angles 
produced into short narrow horns ; space between the horns 
convex, divided into a large central and two lateral smaller 
lobes ; structure punctate, the puncta becoming smaller to- 
wards the angles. (Fig. 7.) 
Hah. Barbadoes deposit, Cambridge estate ; in slides com- 
municated by C. Johnson, Esq. 
Although I have this pretty species with the frustules 
in sitUj I have not been able to detect the very least trace of 
spines at the apices of the horns. There can, however, be 
scarcely any doubt regarding their existence in more perfect 
examples. The puncta are much larger, and more sparse 
in the middle of the valve, which give it quite an ornate 
appearance. 
Hemiauius pulvinatus, n. sp., Grev. — Rectangular; valves 
closely and minutely punctate, the angles produced into short 
narrow horns, tipped with a spine at the inner angle ; space 
between the horns concave, the concavity interrupted by a 
large cushion-like projection. (Fig. 8.) 
Hab. Barbadoes deposit, Cambridge estate; in slides 
communicated by C. Johnson, Esq. 
Chiefly distinguished by the close and minute punctation, 
and by the large single projection, the convexity of which is 
