1901] MICROSCOPICAL JOURNAL. 313 
of the band seems absolutely homogeneous (fig. 5). In 
continuation of the band anteriorly, there is a slit in the 
valve which runs up to the anterior margin near the an- 
terior dorsal angle. The edges of this slit are normally 
in contact, but may be easily separated by pressure. The 
slit’ seems to be produced by the falling out of a number 
of pieces of chitin (fig. 6), exactly in the same way as I 
have described in the case of the line of separation along 
the ventral edge of the ephippium and round the valve 
margins in Leydigia acanthocercoides. The pieces of 
chitin no doubt represent modified hexagonal areas of the 
original shell sculpture in the same line as the series 
which produce the lateral band. In connection with this 
it may be pointed out that the anterior end is often seen 
to be separated from the rest of the band by a transverse 
line {fig. 1). At its posterior end the lateral chitinous 
band appears to end abruptly in the ordinary shell mark- 
- ings. 
In Bosmina longirostris the lateral bands do not pro- 
ject.very much beyond the surface of the shell, but in a 
species (fig. 8) from Upper Lough Erne (probably Bos- 
mina lilljeborgi Sars, although this is perhaps only a 
variety of B. coregoni Baird), very kindly sent to me by 
Mr. W. F. de V. Kane, the projection of the lateral bands 
is so pronounced that they deserve to be termed ridges 
(fig. 9). The position of the bands in this case is also a 
little different to what it is in B. longirostris. As will 
be seen by a comparison of fig. 8 with fig 1 and 4, there 
is a rather greater distance between the lateral bands and 
the back of the shell in B. lilljeborgi(?) than there is in 
B. longirostris ; and more important still, the lower ends 
of bands approach very much nearer to the posterior ven- 
tral angle of the shell in the former than in the latter 
species. I may mention here that the lateral bands are 
not always so evenly curved as shown in the figures, but 
that they sometimes exhibit rather abrupt bends—as ifin 
