POLYC1LETA-BENHAM. Ill 



The thoracic region presents a much wider range of variation as to the number 

 of component segments than do those in Group A. Of those examined I find the following 

 numbers : 



Six have 8 segments. 



One has 9. 



Three have 10. 



Three have 11. 



Five have 12. 



Three have 12 on the right side and 13 on left. 



One has 14. 



Two have 15. 



One has 14 on the right side and 10 on the left. 



There is no apparent relation between the length of body and that of thorax, for 

 in three worms measuring 170 mm. two have 8 thoracic segments, and one has 12. 



Eight segments occur, also, in a worm 135 mm. long; 11 segments occur in a 

 worm 195 mm., while another of the same length has 14 segments. 



In two smaller worms of this group, measuring 72 and 85 mm., I find that the 

 thorax contains only 8 segments. It seems, then, in a very general way that the number 

 of thoracic segments increases with the size, that is the age, of the individual. 



The gills contain a much larger number of filaments than in the typical form of 

 the species. Thus, there are thirty to forty filaments on each side; but in a worm 

 170 mm. long, I find only twenty-one filaments. 



The pigmentation of the gills is liable to much variation also. In some they are 

 uniform in tint, or rather uncoloured; in others there are the usual irregularly arranged 

 splashes of red-brown along their length. In one case I noted that some of the dorsal 

 filaments are without pigment, though most of them have a band of brown extending 

 from the tip to about quarter the length ; or even further down in the more ventral 

 filaments. A few o! them have in addit'on a short transverse band about half-way 

 down. 



In another individual there are three fairly regularly disposed patches at quarter, 

 half, and three-quarter of the length from the base upwards, while the apex is, as usual, 

 uncoloured. 



Others, again, have more numerous distinct bands up to eight in number. One of 

 the smaller specimens has purplish pigment arranged in irregular dots at wide intervals 

 apart along the filaments. 



Probably, had one only a few of these larger worms before one, a new species 

 would have been warranted, but I prefer to leave these in the present species. 



