TRICERATIUM AND CHATOCEROS. 155 
an end view, the frustules are trilobed, the sides of the 
lobes are irregularly indented, and the valve exhibits the 
appearance of being composed of a series of thin layers of 
silex. In the filamentous state, the frustules are narrower 
than those of Triceratium undulatum ; and there is an ellip- 
tical opening between them on each side. 
Triceratium radiatum and Tr. Marylandicum (described by 
me, ‘Quart. Journ. Microsc. Soc.,’ vol. iv), present in 
the centre of the triangular end the appearance of a pseudo- 
nodule, and are probably filamentous, and of the same habit 
_as the two species already described. These species form a 
section or sub-genus. 
TRICERATIUM. 
§ Filamentous. 
—_ 
. T. undulatum.  Frustules with a horn running from the 
eentre of each end. 
T. malleus, n. sp. Valves three-lobed; the lobes of 
unequal length. 
T. radiatuin ? 
. LT. Marylandicum ? 
ee 
op 
CHA&TOCEROS. 
By the kindness of Dr. Wallich, I have been favoured with 
perfect specimens of the species of Chztoceros named by me 
Ch. Peruvianum (see vol. 11. p. 5), and which I had before 
only seen in fragments detected in guano from the Chinca 
Islands. Dr. Wallich’s specimens were taken from the sto- 
machs of Salpz found in the Indian Ocean, and they afford 
the only opportunity hitherto presenting itself of studying 
any species of this genus in a perfect state. 
The body, if 1 may so call it, of Ch. Peruvianum is com- 
posed of two segments which are not symmetrical, the anterior 
segment being (as described in the former paper) semicircular 
at the end, and furnished with two horns, which take their 
origin from two stout shoulders bending towards each other, 
leaving a hollow space between them, and then recurve at a 
right angle, and run tapering out to a very great length. 
This anterior section may properly be called the head, the 
other or posterior section being truncate, and terminating 
also in two long horns proceeding from the inner part of the 
segment. All four horns are of equal length, stoutly sili- 
ceous, spinous, and tapering. 
