NEMERTINES OF PLYMOUTH SOUND. 15 
colour and marking, and they, on the other hand, are singularly 
invariable. 
‘The length ranges from 5 mm. to 1 cm. The body is rounded, 
and ends abruptly both anteriorly and posteriorly as in 7’. dorsale ; 
the head, however, is more apparent than in the latter, owing to 
the shght amount of pigment there distributed. The ground colour 
is yellow, with a sprinkling of orange-red granules, which are strongly 
concentrated in the median dorsal line, forming a stripe of chocolate 
colour, beginning just in front of the anterior pair of eyes, and passing 
backward to the posterior end of the body. 
The eyes are black, and similarly situated to those of J. dorsale. 
Many specimens have been found in the coralline pools at Wembury 
Bay, and they are also met with among the weeds in the second and 
third zones, and dredged at the Duke Rock. In all these places they 
are associated with other species of Tetrastemma, including T’. dorsale. 
15. T. canprpum, O. F. Muller, Oersted. 
Agrees with the remaining species of this genus, and differs from 
the last three in its more or less flattened body, in marked contrast 
to the rounded body of J’. dorsale and its allies, and in its sharply 
separated spathulate head. The species now to be considered are 
also characterised by their excessive variability. Only one specimen 
resembling the type form of McIntosh has been obtained; this was 
found by Mr. Garstang in sand between tide-marks at Rum Bay on 
the 21st of July. 
The reddish and yellow varieties are not uncommon. They are 
found, though in small numbers, in Cawsand Bay among the weeds. 
Larger specimens are dredged in 5—20 fathoms, and they appear 
to be more numerous at the greater depth. Thus specimens have 
been dredged at the Duke Rock, and in Millbay Channel, but the 
majority have come from Stoke Point, where they seem to live 
associated with Lepralia, which they closely resemble in colour. The 
positive points characterising this species seem to consist in the 
shape of the head, which is more rounded than in the other members 
of the genus, in the definiteness of the cephalic grooves, which give 
the head a very characteristic appearance, and in the clearness and 
distinctness of the eyes, which are round and black. But in these 
as in other points there is great variation, and some varieties seem 
to form a series bridging the gulf separating this from the succeeding 
species. An interesting instance of this variation was exhibited by a 
Tetrastemma obtained in October, and which, while agreeing with 
the reddish variety of the present species in all other points, differed 
with regard to the anterior pair of eyes, which, instead of being 
