1893 - 94 .] Dr Gilchrist on Pallial Complex of Bolahdla. 267 
This is proved by the absence of this gap in other Dolahellce. A 
large Dolahella from Samoa in the British Museum showed particu- 
larly well the continuation of the fold over this point without any 
gap. This fold, therefore, must be considered as a continuation of 
the mantle. The changes that it undergoes in its course along the 
floor of the pallial cavity till it merges into the genital furrow are 
shown by fig. 3 A, B, C, D, E, E, which are transverse sections of 
it at various places. It will be noted that a special secondary fold 
which covers over the hypobranchial gland is developed on the 
under side (B, /'), the part directed upwards soon disappearing. 
Another fact to be noted in the general structure of the mantle 
is the limited extent to which it is reflected over the shell, thus 
leaving a large portion of the latter exposed (fig. 2, sh). This is 
exceptional among the Aplysiidce, where the shell is as a rule 
almost completely covered by the reflected mantle. As in the 
Aplysiidce, the under side of the mantle is crowded with peculiar 
large unicellular glands (fig. 4, gl, fig. 2, gl). A slight fold (fig. 4, /, 
fig. 2, /), the significance of which is not very apparent, is also 
to be noted. It becomes much larger towards the posterior end of 
the mantle. It does not appear in Aplysia. 
The shell is peculiar in shape and calcification, but presents no 
specially important features. As a faithful record of the course of 
development of the mantle it reflects the peculiar shape of that 
organ, and especially that part of it modified into an exhalent 
organ, the sipho. 
The osphradium presents characteristics which again bring the 
animal nearer Notarchus. I have elsewhere figured and described 
the peculiar lid or fold of skin in Notarchus, whereby the osphradium 
can be completely covered up, and suggested that this may be con- 
nected with the fact that not only the pure incoming stream of 
water, but also the impure outgoing stream, pass over this sensory 
organ, which by this fold may be protected from unnecessary irrita- 
tion. An arrangement much similar to this, though differing in 
details, occurs in the form under examination and may perhaps be 
satisfactorily explained in the same way. Fig. 5, a section through 
the mantle (m.) and efferent vessel, on the under side of which 
the osphradial pit occurs, shows this. The lip or fold of skin (fig. 
5, osd.) is well marked. The peculiar state of the osphradial ganglion 
