Wenham^ on the Fracture of Polished Glass Surfaces, 105 
more recent knowledge regarding the frequency of 4 — 6 
angles in aberrant forms of genuine Triceratia, and in the 
absence of any structural peculiarity^ I have no hesitation in 
placing these diatoms in the genus Triceratium. 
Triceratium polygoniwn, n. sp.^ Grev. — Large; valve with 
6 somewhat rounded angles and straight sides ; surface filled 
with remote radiating lines of granules^ except in the centre, 
which is faintly reticulate; margin strong, striated. Dis- 
tance between the angles -0022''. (Fig. 14.) 
Hab. Among ballast, at Stoneferry, near Hull ; George 
Norman, Esq. ; cabinet of F. Kitton, Esq. 
An interesting form, evidently allied to the preceding, but 
differing in its larger size, smaller and more distant granules, 
and especially in the strong, rather broad, striated border. 
Amphitetras. 
Amphitetras nobiUs, n. sp., Grev. — Valve very large, with 
broad, somewhat ovate lobes or angles, and concave sides; 
centre depressed ; surface filled with large, roundish or 
roundish-quadrate, radiato-concentric granules; angles ter- 
minating in short tubular processes. Distance between the 
angles -0052^^ (Fig. 27.) 
Hab. In dredgings from the Red Sea ; L. Hardman, Esq. 
A magnificent species, and one of many undescribed novel- 
ties contained in my friend Mr. Hardman^s cabinet. The 
form of the lobes or angles, and short tubular apices, appear 
to be amply sufficient to separate it from A. antidiluviana, to 
which it is most nearly allied. 
Notes on the Fracture o/ Polished Glass Surfaces. 
By F. H. Wen HAM. 
(Read June 14, 1865.) 
The short communication which I submit to your notice 
scarcely merits consideration as a discovery; but as the 
microscope has in this case immediately detected the cause 
of a well-known phenomenon, I bring it forward as an ex- 
ample of the use of the instrument in practical investigations. 
It is a fact known to the philosophical instrument makers, 
that if a metal wire be drawn through a glass tube, a few 
hours afterwards the tube will burst into fragments. The 
VOL. XIIT, 
