WALLICH, ON TRICERATIUM. 249 
figured in the same place, under the sub-tribe with “angles 
spinose,” is much smaller, has nearly straight sides, but ex- 
hibits “a projecting fringe, stated to consist of oval depres- 
sions.’ Specimens of T. comptum in my possession, obtained 
from Californian guano, clearly correspond with Mr. Bright- 
well’s, and corroborate the distinctions from T. fimbriatum. 
Mr. Roper, in the Journal of the Society for July, 1854, 
p- 283, gives a figure also of T. comptum,'Ehr., which he 
states as having “a row of cells projecting above the margin 
of the valve ; sides straight or slightly convex, the horn-like 
processes short and obtuse; and cellular structure large.” 
But although Mr. Roper is doubtful whether his specimen 
may not be a young form of 7. favus, he leans to the opinion 
that the length of the angular processes and fringe-lke row 
of cells appear to give it a distinctive character. 
The next form is from brackish water in the Delta of the 
Ganges, and is undoubtedly new. I propose to call it 7. an- 
nulatum. The characters are—Valve minute, triangular ; 
angles slightly produced, rounded; sides shghtly concave ; 
tri-radiate, and having its surface covered with minute 
puncta; the more close aggregation of which, in concentric 
rings around the common centre, gives the valve an un- 
dulated appearance. 
The rays are thickenings of the siliceous epiderm which 
pass from the centre of the valve outwards in the direction 
of each angle, gradually becoming fainter as they approach 
the latter. In lke manner the puncta are more numerous 
and are more closely aggregated as they approach the central 
portion; whilst, at the extreme angles, the markings are 
almost entirely wanting. 
Diameter of each side -002. 
The next species, which I propose to call T. pentacrinus, 
although normally a five-sided form, is also distinctly refera- 
ble to that genus. It was obtained off St. Helena, in thirty 
fathoms water, in a living condition. The characters are 
as follows : 
Frustule free, constitutmg a pentangular prism; valves 
somewhat convex, pentangular, each side deeply convex ; with 
short stout cornua at each angle. Surface spinous; divided 
into compartments, by interrupted bands, which radiate 
irregularly from the centre, and inosculate laterally with 
each other. Cellular structure minute, consisting of circular 
dots. Connecting membrane annulate, indefinite, marked 
with dots arranged in quincunx, and which become more 
minute as they advance from the margin towards the median 
line of the annulus, and are partially interrupted at the 
