L.M.B.C. TURBELLARIA. 73 



light-brown, and mottled dark-brown specimens occur. 

 On the ventral smiace 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. Alcinoi, 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 20 fms. 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 

 are the following : —Firth of Forth, St. Andrews, east 

 coast of Ireland, Aberystwyth and Plymouth. 



