148 
WesTj on Diatomacece. 
nences ; surface uniformly punctate^ with a single row of 
larger puncta along the apposed margins. Cmgulum covered 
with fine^ regularly decussating puncta. Length of valve^ 
from central point of one angle to that of another_, -0025." 
In Barbadoes earth, very rare. 
This species approaches TV. venosum, Br., TV. coniferum, 
Br., and TV. trisulcum, Bailey. From the former it is 
separated by the absence of the conspicuous lines; from 
T. coniferum by the concave sides, the obtuse angles, the 
lines separating these from the body of the valves, and by 
the absence of spines ; from T. trisulcum, by the circular 
form of the angles, and the regular and close punctation. 
It is a robust and well-characterized form ; the discovery of 
further examples may be expected to repay careful search in 
the rich material that yielded the present one. Each ob- 
tusely rounded angle, on front view, bears a not inapt 
resemblance to a lady^s thimble, with its regular rows of 
diagonally arranged depressions. 
T. marginatum, Br. (Fig. 4.) 
Front view ; valve very shallow, much depressed in the 
centre, elevated at the angles into short truncate horns ; 
margin of valve with a delicate ala, unto which the puncta 
and canaliculi are continued ; apposed edges broadly free 
from markings, as in the last ; cingulum ? 
The various aspects of the three above-mentioned forms 
were obtained by moving the specimens about by gentle 
pressure on the covering glass, the balsam, of course, not 
having been hardened; this plan may be strongly recom- 
mended when examinations are made of material in which 
fine forms occur but sparingly. 
The two species of Triceratium not having been fully 
described, I am induced to make the following remarks, 
with the hope of rescuing them from the confusion in which 
they are enveloped, some excellent observers still classing 
them as varieties of one and the same species. 
T. intricatum, T. W. (Fig. 5.) 
" Valve with acute angles,^^ centre tumid, angles slightly 
produced ; " cellular structure faintly discernible an ap- 
parent pseudo-nodule due to a short central spine ; margins 
of frustules undulated, commonly presenting an end view, 
united in distant series to form a filament. 
This species was described and figured in the first volume 
of the ' Synopsis of the British Diatomacese,^ as T. striolatum ? 
Ehr. When it was ascertained that it was not that species, 
the form of the margins readily suggested the name ^' undu- 
latum ;" but that it is not the " undulatum^^ of Ehrenberg. 
I think certain, though to separate them by description is 
