990 MR. F A. POTTS ON 
from that of another species, but the point I wish to emphasise 
is that the sete of the fourth parapodium vary greatly, and a 
statement as to their character can only be made after examination 
of a large series of individuals. It has been shown in the 
preceding part of this section that the other sete of the anterior 
region are always variable, and it would have been rather 
surprising if those modified setze which are found in the fourth 
parapodium had been found to belong to types fixed for each 
species. 
Text-figure 13, 
A, B. Phyllochetopterus elioti. C. P. pictus. 
Enlarged sete from 4th segment. 
Some Remarks ON THE GENERA Spicchetopterus AND 
Phyllochetopterus. 
Until 1856 Chetopterus was the only member of the family 
known, but in that year Michael Sars (10 a) described ‘the 
genus Spiochetopterus to include a species (S. typica) from 
Norwegian waters, which differed from Chetopterus in possessing 
long peristomial tentacles. In 1863, Grube (7) instituted a third 
genus, Phyllochetopterus, for a worm from the Adriatic. But the 
two forms are undoubtedly similar, and de Quatrefages, in his 
‘Histoire des Annélés,’ goes so far as to include Grube’s polychet, 
P. gracilis, in the earlier genus Spiochetopierus. 
Spiochetopterus typica was described as living in a jointed 
transparent tube. It has long peristomial tentacles, but a pair of 
