250 WALLICH, ON TRICERATIUM. 
angles. Around the margin a row of oblong cells, placed 
side by side. 
The peculiar ribbed character here seen is conformable to 
that shown, in a modified degree, in several already described 
species. For instance, in the J uly number of the Society’s 
Journal for 1856, Mr. Brightwell characterises and figures 
no less than nine forms, all of which present the ribbed 
structure more or less. ‘To these markings, in some of the 
forms, Mr. Brightwell applies the term of “ canaliculi’? In 
the form under notice now, the ribs are, however, simple 
thickenings of the siliceous epiderm, which are neither 
tubular, nor dip down at all into the cavity of the frustule, 
so as to form pseudo-septa. The puncta are arranged im rows 
following the radiate direction of the ribbed partitions 
referred to. The horn-like processes appearmg more like 
inflated prolongations of the angles of the valve, the apices 
being minute and capitate. Valve constricted deeply between 
the bases of the horns and its margin. Spines numerous, 
irregularly placed, short and furcate. Connecting membrane 
projecting boldly, hyaline, with the undulating outline given 
by the form of valve, and its concave margins Anflecteds 
Diameter of frustule -0023; depth about -0020. 
T have met both with four- and six- angled varieties of this 
species; but these are rare. ‘The first is not unlike that 
figured by Mr. Shadbolt in the Society’s Journal for October, 
1853, p- 17; but as the front view is not given, it is 
difficult. to say positively whether the two are identical. 
Mr. Shadbolt describes his species as ‘‘ having the margins of 
the valves considerably hollowed out or emarginate, and 
folded over so that each valve is not unlike in form to a 
collegian’s cap. The surface being elegantly but somewhat 
irregularly ornamented with delicate markings.” 
Two remarkable Diatoms remain to be described in this 
paper, the characters of which, I believe, are essentially new. 
For although, at first sight, one of the species appears allied 
to the filamentous T7riceratia, its marked identity in structural 
peculiarities with the second, which is obviously distinct, 
leaves no reasonable doubt on the subject. 
Again, the second form, under a cursory examination, 
might be referred to Biddulphia, but its ‘unquestionable 
affinity, as I apprehend, to the first, would, with equal force, 
separate it from that genus. In both cases another and ver y 
conclusive example being afforded of the small real value 
that attaches to definitions based on mere outline. 
The species to which I allude were obtained by me from 
the Gangetic Sunderbunds, in brackish water, well within 
