610 PY He (GRAV Bie. 
ventral surface of the anterior end see fig. 3. I am not able 
to give a detailed description of the dorsal surface of the 
head; asin Spionid A, however, the prototroch does not 
extend across it, but is incomplete dorsally as well as ven- 
trally. At the sides of the head the prototroch is carried out- 
wards as a line of 60, cilia on to the bases of the tentacles ; 
in this Spionid D differs from Spionid A, but resembles 
another common form (Spionid B), which I am unable to des- 
cribe in detail ; in general Spionid B resembles Spionid A, 
however. From the bases of the tentacles the prototroch is 
continued downwards as a line of comparatively short cilia to 
the outer and posterior angle of the ciliated area of the 
external surface of the lips. ‘These cilia were not seen in a 
position to allow of their length being determined, but they 
appeared to be of about the same length as those (204 
long) of the ciliated area of the external surface of the 
lips. I was unable to determine with certainty whether this 
row of short cilia was quite continuous with the long cilia of 
the prototroch or not. 
Polydora A. 
As an example of the Polydoridzs we may take this, the 
commoner of the two species of Polydora iarve found at 
Port Erin during July. A specimen of Polydora B appeared 
to agree closely with Polydora A in the arrangement of the 
cilia; during life I was only able to examine the ventral 
surface of this specimen however. ‘The differences between 
the Polydora larva and Spionid A are differences of 
detail only. Of those of the ventral surface one of the most 
striking is the presence of gastrotrochs, not on every seg- 
ment, but only on segments posterior to the first and denoted 
by “odd” numbers, except in the neighbourhood of segment 
10, which bears these cilia, whilst segments 9 and 11 are 
devoid of them, like the ‘even ” segments of the rest of the 
body. Another difference that may be noted is the shortness 
of the neurotroch, which does not extend as far back as even 
