NEMERTINES OF PLYMOUTH SOUND. 19 
spicuously darker than the median portion. This tendency is 
expressed more strongly in some specimens than in others, until a 
condition is reached in which the median portion has almost entirely 
disappeared, leaving only a thin bridge which joins the posterior 
ends of two masses of pigment which extend from the anterior to the 
posterior eyes. Behind the pigment bridge there is a band of white 
separating it from the posterior eyes, but there is no white on the 
anterior portion of the head. A median aggregation of granules is 
present on the body, forming a white dotted line passing from the 
white head patch to the tail fan. 
A specimen which was dredged in the Hamoaze near the “ Royal 
Adelaide”? on December 14th represents the final term of the series, 
and follows the last very closely. In this individual the pigment 
bridge has completely broken down, so that in this case the head is 
characterised by two dark patches passing from the anterior to the 
posterior eyes, one on each side. Between the posterior eyes there 
is a patch of white, but this is much smaller than in the last speci- 
men. ‘The posterior eyes are slightly smaller than the anterior 
(which was the case in the last variety), and are slightly closer 
together. This individual undoubtedly belongs to this species, both 
on account of the fact that it belongs to an entire series reaching up 
to the type form, and also because in the presence of the white patch 
between posterior eyes, in the shape of the head and the condition 
of the stylet region of the proboscis, it exhibits most characteristic 
melanocephalous features. Nevertheless this arrangement of pigment 
is certainly suggestive of a transition towards 7. vermiculatum, and 
especially recalls varieties described as intermediate between T. can- 
didum and T’. vermiculatum. 
Only one case has come under my notice in which any relation 
could be detected between the colour of the animal and that of 
its surroundings. It was that of a specimen found among red 
weeds. The colour of this individual was remarkable, differing 
entirely from any other met with. The ground colour was a green- 
ish yellow, but this was covered superficially by minute red-brown 
pigment granules, the result being the production of a colour remark- 
ably similar to that of the weeds in which it was found. The red- 
brown granules were concentrated on the head to form the usual 
quadrate patch, the edges of which were not sharply defined, and 
the patch itself was reddish, not black. This animal, which was 1 cm. 
long, was a female containing ova. 
18. T. ampiguum, n. sp. 
Under this name I include a few specimens found in November 
which have many points of agreement with J’. Robertianx, as a 
