76 Transactions of the Royal Microscopical Society. 
newly formed half-frustule could possibly, in its case, be fully 
developed within the body of the parent valve, or even that it 
could be secreted in the pulpy state within it. A glance at the 
admirable figure of this diatom in ‘The Synopsis’ will at once 
confirm this view.* 
A similar configuration, but even more conspicuous, may be 
observed in B. regina and B. Tuomeyii (a variety of B. regina). 
In B. Baileyii the frequent extension of the connecting zones 
considerably beyond the extreme point occupied by the faces of the 
newly formed valves is very marked. But in this species, as in 
B. turgida, the constriction is slight, though sufficiently distinet 
to be easily perceptible. Amongst the rarer filamentous genera 
showing these characters strongly, may be mentioned Dicladia and 
Cletoceros. Indeed, were it not that the presence of the connecting 
zone in every diatom furnishes us with a character which is almost 
infallible, the true affinities of these two genera might remain 
doubtful. The same may be said of Ehizoselenia, in which I 
detected the connecting zone, but with considerable difficulty, 
owing to its extreme attenuation, and only in the uncleaned state. 
As a matter of fact, there is a constriction or notch, into which 
the inflected rim of the connecting zone is received, present in 
probably every diatom, though much more difficult of detection 
in the minute elongated and tabular forms. Hveryone who knows 
the Diatomacex is acquainted with the appearance presented in the 
front view of their frustules, at the four points or angles where 
the connecting zones are in contact with the valvular margin. 
The notch always visible in that position is in reality a profile view, 
at that point, of the groove and the inflected rim of the connecting 
zone that fits into it, being totally distinct from the lateral view of 
the terminal nodule which holds a neighbouring position. Here 
again I would invite attention to the figures in ‘ The Synopsis,’ as 
admirably depicting the structure. 
I must here allude incidentally to a very important fact con- 
nected with the extra-frustular appendages of the diatom, viz. my 
having found that the principal spines (not the cornua) on the 
valves of some Biddulphiz, and the spines forming the elegant 
coronet on those of Creswellia, are tubular. In this respect they 
resemble sponge spicules. But it can be at once seen in B. turgida 
that these spines, instead of being secreted in concentric films 
around the longitudinal core or axis (which is the invariable mode 
of growth in the siliceous sponges), are perfectly homogeneous, 
and in this respect assimilate with the Polycystina. In B. turgida 
* My observations on these big diatoms were chiefly made at Guernsey in 
1858, where they are to be found at depths ranging from half low-water mark 
to eighteen or twenty fathoms. I was gratified to find, whilst this paper was 
being drawn up, only a few days ago, that the characters referred to are admi- 
rably shown in ‘The Synopsis’; notably B. turgida, also a Guernsey diatom. 
