TURBELLARIA OF PLYMOUTH SOUND. 31 
the fauna. I should state that for several reasons my attention was 
directed more particularly to the Rhabdoccelida, consequently the 
number of Polycladida here recorded will, in all probability, be 
increased by future investigation. 
As regards the methods of collecting the Turbellaria, it 1s neces- 
sary to bear in mind that almost all the Rhabdoccelida are so minute 
(rarely more than 2 mm. in length) as to render it a matter of the 
greatest difficulty to isolate them from the tangled masses of sea- 
weed in which they are usually found. My method of working the 
area between tide-marks was twofold. I collected the Ulva, Ptilota, 
Bryopsis, and other weeds, and placed them in vessels of sea water 
in the Laboratory. The Rhabdoceeles emerged in great numbers, 
especially towards night, and could be picked out with a pipette. 
Stones richly coated with ascidians, polyzoa, sponges, &c., and the 
sand- and shell-débris at the base of Corallina, treated in a similar 
manner, were very productive. The drawback to this method is 
that the real habitat of any particular species cannot thus be deter- 
mined ; and although I attempted to isolate the various kinds of sea- 
weeds I was not successful in establishing a constant relation 
between a Turbellarian and the plant on which it is found. 
My second method was that proposed to me by David Robertson, 
Esq. It consisted in the use of a hand-net, in the mouth of which 
a sieve was placed to prevent the entrance of bulky weeds. Such a 
net was used from the dinghy at low water among the Laminaria, 
Halydris, &c., which border the creeks in Wembury Bay, the Break- 
water, and other places. Tide-pools were also explored by its help. 
The dredge brought up a large number of interesting forms. Millbay 
Channel, the Hamoaze, the Duke Rock, and the New Grounds 
are especially productive in infra-littoral forms. Examination of 
dredge-material at night gives one a vivid idea of the activity and 
voracity of this group. Pelagic forms were rare, and chiefly repre- 
sented by the larve of Leptoplana and Miiller’s larve. The latter 
were specially abundant in October. 
DIsTRIBUTION OF TURBELLARIA IN ZONES oF Depru. 
First Zone.—This zone is usually uncovered for one to two 
days during neap-tides. Monotus fuscus is here the characteristic 
form, although it ranges throughout the tidal zone. It appears to 
derive moisture from Balani into which it creeps during ebb-tide. 
Other interesting devices for gaining moisture are recorded by Hallez 
and v. Graff. Towards the lower portion of this zone Convoluta 
paradoxa occurs. 
