Greville, on New Diatoms. 29 
somewhat flattened. It occupies nearly half of the whole 
breadth of the valve^ which is •0025"'. 
Hemiaulus lobatus, n. sp._, Grev. — Rectangular ; valve with 
the angles produced into slender horns, each tipped with 2 
minute triangular teeth ; space between the horns concave, 5- 
lobed ; structure punctate ; 2 lines of very minute puncta 
passing along the horns. (Fig. 9.) 
Hab. Barbadoes deposit,, Cambridge estate ; in slides com- 
municated by C. Johnson, Esq. 
The two lines of very minute dots on the horns, and the 
different character of the teeth which terminate them^ seem 
to indicate a different group of the Hemiaulidce. The central 
projection is the largest, and almost hemispherical. All of 
them are enclosed, as it were, within a concave hyaline 
limbus, which, passing up the side of the horns, ends in the 
little tooth at the inner angle. Breadth of the frustule '0020"'. 
Hemiaulus exiguus, n. sp., Grev. — Minute, rectangular ; 
valve with the angles produced into elongated-conical horns 
tipped with a spine; space between the horns occupied 
with a single convex projection ; structure minutely and 
remotely punctate. (Fig. 20.) 
Hab. Barbadoes deposit, Cambridge estate; in slides com- 
municated by C. Johnson, Esq. 
Rather ambiguous in appearance, having, in some respects, 
the aspect of a Biddulphia ; but the rectangular form, 
and the presence of the little spine at the apex of the horns, 
show a greater affinity with Hemiaulus. Breadth of frustule 
•0011". 
The following diatoms, while they cannot be referred to 
the present genus, appear to belong to the family, and would 
probably constitute two or three genera had sufficient 
materials been at our command. At the same time they are 
so rare, and the probability^ of obtaining an additional supply 
of the particular sample of the deposit in which they occur 
so small, that I think it desirable not to lose the present 
opportunity of making them known. It will be understood, 
then, that the letter " Hy' which stands before the specific 
name, represents merely the family; or, if it be thought 
preferable, for formes sake, it may represent the genus 
Hemiaulus, with more than one mark of doubt. 
H. tenuicornis, n. sp., Grev. — Very minutely punctate, not 
wholly rectangular ; valve with the angles produced into very 
long, slender, incurved horns ; space between the horns nearly 
straight, with a slight central projection. (Fig. 10.) 
