WesTj 071 Diatomacece. 
153 
stituting a new genus for it there can be no question,, and I 
have much pleasure in dedicating it to Mr. Atthey, a very 
acute and diligent observer. It is not so easy to decide on 
its true place in a natural system ; for it appears to unite 
Striatella with Chcetoceros, next to which latter I feel dis- 
posed to place it, on account of the spinous processes at the 
angles ; and the discovery of the structure of Rhizosolenia, a 
near ally^ in which I ascertained the existence of indetermi- 
nate alternately- arranged annuli^ seems to diminish the diffi- 
culty that might otherwise be felt in allying it with Chce- 
toceros. 
6. Closterium, Nitzsch. 
C. aciculare, n. sp. 
Frond elongated, very slender, straight except at the extre- 
mities, which are very slightly curved downwards, gradually 
tapering from the centre to the very acute ends. Length of 
frond, -V^h of an inch; greatest breadth, ^-^^Q^th, (Fig. 16.) 
This form does not agree with any species of Closterimn 
given by Mr. Ralfs; from Cjwncidum, to which it approaches, 
it differs in the gradual tapering from the centre to the very 
slender produced ends. Mr. W. Archer, of Dublin, has 
kindly sent me tracings of some slender Closteria, figured 
by De Brebisson, with a note, from which I extract the 
following : — 
" It is far longer in proportion to its width than any Clos- 
terium I have ever seen, either living or figured. Is the 
empty frond smooth or striated? Are the strise close and 
fine or coarse ? Its great length and slight breadth bring it 
near C. pralongum (Breb.), but in that species the ends are 
slightly turned upwards; in that respect, like C. turgidum, 
yours look downwards, rather. Its general outline more 
approaches C. macilentum (Breb), which is, however, little 
more than half as long as yours in proportion to its width. 
Both those species are smooth, i. e., without striae. Has Mr. 
Atthey seen its conj ugated state ? In C. macilentum the 
empty frond remains attached to the sporangium for some 
time ; conjugation takes place soon after self- division, so 
that one empty segment of each old frond is much longer 
than the other." 
In reply to these questions, though sporangia have been 
found with it, their connexion has not yet been traced, and 
the empty frond is non-striate. It was found by Mr. Atthey 
in abundance on Prestwick Carr, Northumberland, a noted 
place for these organisms, which, however, there is too much 
reason to fear, have now entirely disappeared from it, owing 
to the drainage of the spot. 
