ON PHORONIS OVALIS, STRETH1LL WRIGHT. 
141 
by some authors of a relationship between these two groups. 
The Plioroniclea differ from the Polyzoa in their embryonic 
development, as well as by striking morphological characters, 
and in view of these differences the resemblance of the 
invaginated body-wall to the tentacle-sheath of the Polyzoa 
seems to be merely a fortuitous one. The formation of an 
introvert containing the retracted lophophore might perhaps 
be compared with more reason with the similar introvert in 
Sipunculoid Gephyrea, though the affinity of the Plioronidea 
to that group has not been established with any certainty. 
The introvert of these specimens of P. oval is is not unlike 
that which occurs in certain Gasteropoda (e.g. Buccinum), 
but it would hardly be maintained that this resemblance is 
any indication of affinity. 
The Larval Form of Phoronis ovalis. 
Although the observations here recorded do not throw any 
direct light on this question, one or two remarks on the sub- 
ject may not be out of place. P. ovalis is known from 
Strethill Wright's original account to occur in the Firth of 
Forth, while the large number of individuals found by me in 
a single shell from the Northumberland coast suggests that 
the species is common along the eastern coast of the northern 
part of Eugland, although it has hitherto been overlooked 
owing to its retiring habits. Actinotrocha has more 
commonly been found in these regions than the adult Pho- 
ronis; and it is, for instance, of frequent occurrence at St. 
Andrews. 
The adult characters of P. ovalis seem to be so distinc- 
tive, particularly the small number of the tentacles and the 
restriction of the bundles of longitudinal muscles to a small 
part of the metasome, that a recently metamorphosed Actino- 
trocha belonging to this species might well be recognisable. 
It should, however, be pointed out that the characters of the 
individual produced by the metamorphosis of a larva may 
differ from those of any of the specimens examined from the 
