BRIGHTWELL, ON TRICERATIUM, ETC. 153 
vessels forming a very free inosculation with each other. As 
they approach the edge of the lens, which at this period does 
not fully reach the margin of the capsule, and is somewhat 
irregular at its cireumference, they have a tendency to run in 
pairs, and pass directly straight over the edge on to the 
anterior surface of the capsule, where they again spread out 
and form a stellate network ; but at the period of birth not 
so free as upon the posterior capsule; here they imosculate 
with other branches derived from the ciliary processes and 
iris, which at this period of life is in contact with the lens, 
FurtHER Opservations on the Genera Tricreratium and 
Cuatocreros. By T. Bricurwent, F.L.S. 
My former papers on these Genera have been chiefly 
confined to the description of species, and are necessarily 
imperfect, and to that extent unsatisfactory, in consequence 
of the difficulty of obtaining specimens in a living state. 
The species being all marine, very few opportunities occur of 
seeing them alive, and it is doubtful whether any one of 
them has been seen in a state of conjugation. If, as one of 
our highest authorities (the late lamented author of the 
‘Synopsis of the British Diatomacez’) says, “neither size 
nor outline can be wholly relied on, and striation is the best 
guide for specific character and, when this fails, the arrange- 
ment of the endochrome, or the habitat of the living 
frustule,” it is obvious how few of the described species can 
have been sufficiently known to warrant us in deeming them 
finally established, and how important is every step towards 
attaining a knowledge of the living diatom, and especially of 
its modes of increase. 
The recent discovery that the Diatomacez abound in most, 
if not all, the Tunicata, and even in animals so small as the 
Noctiluez, and that they are often found in those situations 
in a living state, promises to add greatly to our knowledge 
of the marine species. It was from sources of this kind that 
I derived materials for my paper on the Rhizosolenia, and it 
is from gatherings made from Noctilucee, and the stomachs 
of Sulpe, that materials have been obtained, which will, I 
trust, enable us to advance a step further in our knowledge 
of the genera mentioned at the head of this paper. 
VOL. VI. N 
