POLYCHXZT LARVAS. 619 
of one of the larvae for which he created the provisional 
(larval) genus “ Chaetosphaera.” The stout and diverse 
form of the setae, together with the habit which the 
Plymouth larva shares with Spionid D of contracting and 
curling up into a more or less spherical spinose mass when 
irritated, proves conclusively that the Plymouth larva is 
a true “ Chaetosphaera,” and from this it may be inferred 
that the peculiar structure of the head found in the 
Plymouth larva and in Spionid D is one of the charac- 
teristics of the genus. As Hacker was only able to 
examine preserved specimens, it is not surprising that he 
saw nothing of this. ‘The simpler stout setae which alone 
are found in Spronid D bring this larva nearer to the 
species of “ Chaetosphaera”’ figured by Hicker (loc. cit., 
p- 20) im his text-figs. C and D; this, however, bears 
serrate setae anteriorly, whereas the setae of Spronid D 
are all smooth. 
A specimen of another species of “ Chaetosphaera” 
was obtained by Prof. Herdman at Port Erin in April, 
and this he kindly sent on to me; but as it is at present 
only known by this one preserved specimen I cannot give 
a full description. The general form of the body is lke 
that of Spiomd D, but the “snout? is of course 
contracted beyond recognition. Most of the setae 
resemble those of Sproned D in form, but are serrate 
instead of smooth; amongst these a single broad, flat, 
and somewhat curved seta, with rather finely serrate 
edges occurs in some of the dorsal tufts. Though broad 
at the base it becomes much broader distally, and then 
rapidly tapers to a point, the outline of the tip consisting 
of a pair of somewhat concave curves. The eyes are four 
in number. 
With regard to the adult form of “ Chaetosphaera,” 
it is interesting to note that a slender median tentacle, 
