54 
GrEvillEj on New Diatoms. 
the cellules somewhat quadrate, arranged in transverse lines, 
rather larger in the series forming the slightly concave me- 
dian space, becoming punctiform in the horns. (Fig. 22.) 
Hab. Barbadoes deposit, Cambridge estate ; in slides com- 
municated by C. Johnson, Esq. 
This bears some relation to the exceedingly variable H, 
Polycystinorum ; but the uniformity of the cellulation, the 
form of the cellules themselves, and the total absence of ele- 
vations and of transverse costse in the upper surface of the 
valve, have led me to separate it. Length of valve -0040"'. 
Hemiaulus ? ? robustus, n. sp., Grev. — Valve in front view- 
exceedingly minutely punctate, produced at the angles into 
broad, elongated, incurved horns, dilated and rounded and 
turned outwards at the apex, and having a row of puncta 
down the inner margin ; median space concave, with a small 
central elevation. (Fig. 23.) 
Hab. Barbadoes deposit, Cambridge estate ; in slides com- 
municated by C. Johnson, Esq. 
This, of course, is not a genuine Hemiaulus ; and I only 
introduce it as another of the highly curious series of forms 
belonging to the family which the patient researches into the 
Barbadoes deposit have brought to light. It is evidently 
allied to some of those already published in the ^ Transac- 
tions^ of the Society. I have elsewhere remarked that these 
papers can only be regarded as miscellaneous contributions 
to our knowledge of diatoms ; and, with regard to such sub- 
jects as those now before us, unless some record were made 
of their existence, science would be none the better for 
their discovery. Other naturalists will now be enabled, 
under more favorable circumstances, to take up the subject 
where I may be compelled to abandon it. It is already 
obvious, I think, that Heiberg's proposed new family of 
Hemiaulidece will, if it can be established at all, require con- 
siderable revision. The length of the valve of H, ? ? robustus 
is -0020'' ; the length of the horns '0030^^ 
Hemiaulus ? ? capitatuSy n. sp., Grev. — Valve in front 
view hyaline, smooth, the angles produced into erect, thick, 
inflated horns, with large spherical heads; median space 
with a large centrical spherical process, supported on a short 
neck. (Fig. 24.) 
Hab, Barbadoes deposit, Cambridge estate ; in slides com- 
municated by C. Johnson, Esq. ; extremely rare. 
It will not do to speculate too boldly on the immediate 
affinities of this very distinct diatom ; so far only can we 
speak with confidence when we refer it either to the Bid- 
dulphieee or the Hemiaulidece, The apex (or articulating sur- 
