L.M.B.C. TURBELLARIA. 167 
light-brown, and mottled dark-brown specimens occur. 
On the ventral surface the central, plaited pharynx is readily 
seen lying in its sheath. Behind it comes the male genital 
pore, towards which the conspicuous V—shaped area, 
caused by the vasa deferentia, converges: behind this 
again, the female pore. Behind these two apertures is a 
muscular depression, the sucker, which is probably of con- 
siderable use to the animal since it ensures a firm hold on 
the substratum. From the dorsal surface the sacculated 
main-gut and its numerous lateral branches may usually 
be seen. In front, four groups of eyes are generally readily 
distinguishable although occasionally the two groups on 
each side unite, so that their double nature is not obvious. 
The anterior group consists of eyes which, in genera closely 
allied to Leptoplana, surround the bases of a pair of 
tentacles, hence the term tentacular group. The tentacles 
persist in a rudimentary condition in L. Alcinor, Lang. 
The posterior group contains rather larger, more markedly 
reniform eye-specks. From other species of Leptoplana 
which resemble tremellaris in appearance, this species 
may be distinguished by the presence of the sucker and 
by the simple, non-muscular, female genital canal. 
This species occurs at Hilbre Island, Puffin Island, Port 
Erin, and Port St. Mary, on the under surface of weed- 
covered stones between tide-marks. It also descends 
to about 20fms. Young specimens are more or less pelagic 
and differ from the adult in their shape which is almost 
that of a spherical triangle. 
Other localities for L. tremellaris on the British coast 
ave the following:—-Firth of Forth, St. Andrews, east 
coast of Ireland, Aberystwyth and Plymouth. 
