CHJETOPTERUS FROM NORTH WALES. 485 
in the tail portion, each segment having four feet (two to work each way). I estimate 
that on each foot there are not fewer than one hundred of these combs; if so, the tail 
alone would bear 16,000; and the disks, lobes, and other surfaces, which also bear them, 
would go far to increase this number by one-half at least. 
In every tube, without exception, which contains a Chetopterus there is also a parasite 
—an Annelid which corresponds with the description of ** Polynoé” given in Mr. Gosse's 
‘Manual.’* It has bristles of one sort only (long, pointed, toothed like a saw on one edge 
atleast). It has antennze and two pairs of eyes. Its segments are alternately provided 
with soft appendages (in this case the appendages are alternately shield plates and cirri). 
It has two pairs of teeth, or jaws, in an evertile proboscis. In large tubes the parasite 
is larger, less in the small ones. I generally find it crouching on the lower segments of 
the body of the Chetopterus; and the earliest indication of the death of that Annelid is 
the exit of the parasite from the tube. 
In the South Carolina specimens I understand the parasite is always a small crab. 
Near these Chetopteri I find various Terebelle, Cerianthus, Sabella, Mya, in great 
numbers, and a very large Pholas, buried at least a foot and a half in hard soil, and 
having siphons, the open ends of which are nearly two inches in diameter. Should you 
like to have any of these, or any further specimens or information about Chetopteri, I 
shall always be glad to render any assistance in my power to collect information on a 
matter in which there is so much of interest. 
Believe me, dear Sir, yours faithfully, 
JOHN WILLIAMS. 
Dr. Baird, British Museum. 
EXPLANATION OF PLATE XLIX. 
Figs. 1 & 2. Chetopterus insignis, natural size, from a specimen in spirits: 1, dorsal view; 2, ventral ditto. 
: a, anterior portion of body; 4, first segment; c, tentacular cirrus; d, spines of pedal tubercle 
of fourth segment; e, dorsal branch of feet of tenth segment; f, ventral branch of ditto; 
9, middle portion of body ; A, inferior portion of body ; û, ventral feet. 
Fig. 3. Hastate setae of one of the feet of anterior portion of body: magnified. 
Fig. 4. Spine of pedal tubercle of fourth segment: magnified. 
Fig. 5. Fascicle of setze of feet of tenth segment: magnified. 
Fig. 6. Caecum, with faecal matter: magnified. 
Fig. 7. Conical lobe of one of ventral feet: magnified. 
Fig. 8. Seta of ditto: magnified. | 
Fig. 9. Chetopterus insignis, natural size, from a living specimen illu 
Fig. 10. Setz from lateral head-processes (feet of anterior portion of body): magnified. 
Fig. 11. Seta from ventral feet : magnified. 
Fig. 12. Black spine from foot of fourth segment: magnified. 
Fig. 13. Comb-like sete which form the faint line on feet and disks (hooked sete of authors) : magnified. 
strating Mr. Williams's paper. 
* This parasite is a variety of Lepidonotus cirratus. — W. B. 5 
VOL. XXIV. R 
