DR. BAIRD ON A NEW SPECIES OF BRITISH ANNELIDES. 479 
which is almost rudimentary; and the remaining ten are foot-bearing segments. The 
first (fig. 2 b), the rudimentary head, is narrow, with a smooth, thickened border or edge 
which projects a little beyond the rest of the segments at each side. Underneath this is 
the mouth, which is an oblique slit, of considerable size, covered by a flap or projecting 
lobe—the head-lobe of Sars. On each side of it arises a tentacle or tentacular cirrus 
(figs. 1 & 2c), which, like that organ in Spiochetopterus, is of considerable length, and 
furrowed on the inferior surface. In some of the specimens examined these tentacular 
cirri were about 4 lines in length, and coiled round in one or two whirls; in others they 
were more than an inch in length, and laxly floating in the spirit in which the specimen 
was preserved. In Chetopterus pergamentaceus, to which in general form and size this 
species bears a closer resemblance than to any of the others described, these tentacles are 
mentioned by Audouin and Milne-Edwards as being merely a small tubercle, which they 
say might be considered a rudimentary antenna. In Ch. norvegicus, described by Sars 
from the seas of Norway, these cirri (or antennze, as he calls them) are figured as being 
about 1 line long. In the two species described by Stimpson no mention is made of 
these organs at all, while in one only of the two described by Schmarda is there any 
tentacular cirrus depicted. 
In respect of these organs, then, as I have mentioned above, our British species brings 
the genus Chetopterus nearer to the Aricieze naidez, or Spioneze, than any of those pre- 
viously described, and at the same time shows a nearer approach to the Spiochetopterus 
of Sars. 
There is no appearance of eyes. 
The nine segments succeeding the buccal are all narrow, and terminate laterally in 
conical pedal tubercles, which are slightly curved upwards, and vary somewhat in size 
and structure. Those of the first and the ninth segments are the smallest; the inter- 
. mediate ones gradually increasing in length, and reaching the maximum at the seventh. 
Each tubercle is furnished with a transverse row of numerous rather short sete, of a 
yellowish colour, and arranged along its ventral surface. These sets are about fifty in 
number on one of the middle feet, and are strongly and distinctly hastate or spear-shaped 
(fig. 3). The pedal tubercles of the fourth segment are somewhat broader and more 
distinctly marked than the others, and, in addition to the hastate sete, are furnished on 
the ventral surface with a row of stout black spines, which gives the animal a peculiar 
appearance at the first look (fig. 1, d). These spines are about fifteen in number, and 
are situated on the ventral extremity of the tubercle, occupying a portion of the usual 
hastate series of sete. In form they are bluntly emarginate at the extremity, stout, of 
a black colour, and deeply implanted in the flesh of the foot (fig. 4), a portion, not 
above a tenth part of their whole length, being extruded. One or two similar spines 
are mentioned by Sars as occurring in Spiochetopterus—generally only one, but OR 
ally two; and, according to the same author, a series of from four to eight similar 
spines were observed by him in the interior part of the row of sete of the usual 
hastate kind on the fourth foot of Chetopterus norvegicus. They are not mentioned by 
in and Milne-Edwards as occurring in Ch. pergamentaceus ; but Leuckart states 
that similar spines occur both on the fourth and fifth feet of that species. Müller, how- 
3 Q 2 
