4 
stylochus, which 1 intend to call N. viridis. In Fiji I have collected 
a large number of specimens belonging to a representative of a 
new acotylean family, and this interesting Polyclad is a typical in- 
habitant of Melitodes. The two last mentioned, as well as Crozier’s 
Pseudoceros sp., show a great resemblance in colour to that of 
their „hosts“. According to Francotte (1898), this is also the 
case with Cycloporus papillosus when found on synascidians; a state¬ 
ment that I can corroborate from observations in Scandinavia. In 
these cases Ihe pigment originates from the tissues of the „hosts". 
It might be mentioned in this connection that Eurylepta cornuta 
var. melohesiarum Lang (1884 p. 578) and Cycloporus papillosus var. 
laevigatus Lang, found on Lithothamnions (Bock, 1913, p. 264), 
also show a splendid likeness to the substratum. 
The following species are intimately associated with their hosts 
and may thus be considered commensals (sensu lato): Stylochus 
zebra, Emprosthopharynx opisthoporus, Euprosthiostomum adhaerens 
(all three with Pagurids), Hoploplana inquilina in Sycotypus. 
Ceratoplana is a less advanced member of this group. 
Ceratoplana colobocentroti n. g. n. sp. 
(Plate, Fig. 1) 
Locality: Sunda Strait, Krakatau, underneath Colobocentrotus atra- 
tus (L.). 
Mate ri al: Two specimens collected in January, 1922. 
The two specimens of uniform size measured in length 7 mm, 
and in breadth 3 mm. 
The shape of the body is shown on Plate I, Fig. 1. It is a shape 
that often occurs in the genus Stylochoplana, and the presence of 
well-developed tentacles induced me, therefore, to refer this species 
provisionally, before the series of sections were obtained, to this 
genus. The body, which is thin, as in most Lepioplanidae, becomes 
widest in front of the tentacles. In the region of the pharynx the 
margins of the body are nearly parallel. The postpharyngeal part 
of the body is short and quickly tapering (text-fig. 1). 
The tentacles are situated near the limit of the first quarter of 
the body. The rounded shape, which Plate I, Fig. 1 shows, is the 
result of a very decided contraction during the preservation, as shown 
very clearly in the series of sections of the animal. In living 
specimens their real shape is likely to be elongated, narrow and 
