Greville, on New Diatoms. 
27 
HEMIAULID^, fam. nov., Heiber^. 
Erustules uniform (Cellens Skaller ensdanuede), symmetrical in both 
front and side views, rectangular, or nearly so ; as seen in front view pro- 
vided with horn-like processes tipped with one or two straight or inclined 
spines, which are often decurrent ; the horns on their outer side straight, and 
forming a right angle with the base of the valve (Grundflade). Sculpi^ure 
composed of larger and smaller cellules variously arranged, in addition to 
which, costse are often present ; the sculpture of the connecting zone less 
conspicuous. 
Tkibe I. HemimiUdcB gemince. 
Erustules, both in the side and front views, symmetrical in both the long 
and the transverse axes (or, if there be more axes of the same value, 
symmetrical with them all). 
Gen. 1. Hemiaulus, Ehr. 
Valve elliptical (lanceolate oval), produced at the angles (extremities of 
the long axis) into horn-like processes, tipped with a spine. 
Gen. 2. Trinacria, u. gen., Heiberg. 
Valve with a regular triangular outline (having three axes or diameters 
of equal value) ; frustule as seen in the front view with three corner pro- 
cesses, each of which terminates in two spines. 
Gen. 3. Solium, n. gen., Heiberg. 
Valve regularly quadrangular or rhomboid ; frustule, as seen in front 
view with four corner processes, each tipped with two spines. 
Tribe II. Ilemiaulidce cuneata. 
Valve ovate ; connecting zone wedge-shaped ; frustule only symmetrical 
in the long diameter. 
Gen. 4. Corhma, n, gen., Heiberg. 
Valve regularly ovate ; the frustule, as seen in front view with two un- 
equal corner processes, the larger one corresponding with the broad end of 
the valve, each tipped with a single spine. 
Of the above genera, Dr. Heiberg describes and figures 
three new living species of Hemiaulus, two species of Tri- 
nacria, one of Solium, and one of Corinna. I now proceed 
to record the Hemiaulidse observed in the Barbadoes deposit, 
not including the well-known Hemiaulus Polycystinorimi, 
which is abundant. 
He7niaulus reticulatus, n. sp., Grev. — Rectangular ; angles 
produced into short, sharply truncate horns tipped with a 
spine at the inner angle; space between the horns concave, 
with one or more convex projections, cellules minute, hexa- 
gonal. (Fig. 5.) 
Hab. Barbadoes deposit, Cambridge estate, in slides com- 
municated b}^ C. Johnson, Esq. 
This is the only species of the genus as far as I know 
which possesses a true hexagonal cellulation ; the structure 
VOL. xiii. d 
