984 . MR. F. A. POTTS ON 
unmodified trunk-segment. On the other hand, it often occurs 
that trunk-segments fuse with the peristomium and then lose 
their parapodia, with the exception of the dorsal and ventral cirri. 
So that the same process which has affected the peristomium may 
modify the succeeding segments in a similar way. 
The object of this digression is to show that the retention of a 
parapodium in the peristomium of Phyllochetopterus is by no 
means without parallel in other families of Polychets. The 
constancy of the phenomenon makes it of generic value, and 
suggests that possibly the rudimentary notopodium has under- 
gone a change of function which we cannot yet appreciate. 
DESCRIPTION OF A NEW Species, 7. anglica, From Brirish WATERS, 
AND A CoMPARISON OF THOSE SPECIES OF THE GENUS WHICH 
FORM ‘TRUE CoLONIEs. 
PHYLLOCHEZTOPTERUS ANGLICA. (Pl. VI.; Text-figs. 9, 10, 12.) 
Phyllochxtopterus of moderate size (2-12 em. in length), with 
eye-spots. Anterior region with a variable number of segments 
(13-16); @ single enlarged seta in each parapodium of the 4th 
segment. Median region also with a variable number of segments 
(11-25). Tubes creeping; often several run parallel to each 
other, with short lateral connections. More than one individual in 
the same system of tubes. 
Locality. English Channel. 
I obtained this species in March of the present year (1913), 
while working at the laboratory of the Marine Biological Associa- 
tion at Plymouth. Tubs of Chetopterus-tubes were brought in 
from trawlers, apparently obtained from an area a little south of 
the Eddystone. Attached to the Chetopterus-tubes were numbers 
of other very slender tubes, often arranged in parallel bundles. 
Sometimes they were embedded in the substance of the larger 
tube, at other times they were entirely surrounded by large 
colonies of Aleyoniwm, so that it seems that the communities of 
Phyllochetopterus anglica are of comparatively long standing. 
In the character of its colonies this species seems to be inter- 
mediate between P. socialis and P. prolifica, and it will be 
profitable to make a definite comparison :— 
(1) In P. prolifica (Pl. IV.) the colony is usually contained in 
a single, long, stolon-like tube (sometimes bifurcating) with a 
number of very short branches communicating with the exterior, 
and consists of a comparatively large number of smal] individuals 
which reproduce asexually with rapidity (at least in the summer). 
(2) In P. socialis the colony seems to occupy a large number 
of parallel and adherent tubes, the communication between which 
can only be made out with great difficulty. In each mass of © 
tubes the individuals are, however, of the same sex. A single 
tube contains two or three individuals, 
(3) In P. anglica (Pl. VI. figs. 15, 16) the colony is likewise 
contained in a number of tubes, which tend to run parallel, but 
are not,asarule,adherent. The open nature of the colony leaves 
