POLYCH^ETA. 313 



Differs from E. heteroceros in the structure of the operculum, other characters 

 being approximately the same. The branchiae are rather short, the stems stout and 

 close together in a digitate manner, about 16 stems in each gill; terminal filaments 

 slender, flagelliform. Thoracic uncini with six teeth, some with five only. The 

 opercular style is stout, slightly flattened ; the margin of the opercular cup carries 

 23 denticulations ; from the centre of the cup a stout columella rises carrying a circle 

 of eight large hooks, of which the dorsal one is larger than the rest and somewhat 

 scythe-shaped, with a long hook directed ventrally and mesially ; the seven smaller 

 hooks have curved extremities directed outwards and are destitute of accessory 

 processes (Plate VII., fig. 182). The operculum is associated with the right gill ; no 

 rudiment could be found on the left side. The first fascicle contains besides a few 

 simple capillary sctse a bundle of strong unequally bifid setae, the terminal process 

 long and acuminate, the subterminal process very short and obtuse ; these are called 

 bayonet setse (von Marenzeller). 



The Ceylon specimen varies from the type, in which there is a crown of nine hooks 

 instead of eight, and the thoracic uncini show seven or eight denticulations. In spite 

 of these differences, which are not outside a possible range of variation,* the character 

 of the crown of hooks is so distinctive as to leave no doubt as to the identification, 

 notwithstanding the fact that von Marenzeller unfortunately omitted to state 

 explicitly that the hooks of the crown, except the dorsal hook, are directed outwards ; 

 this is left to be inferred, and it is an important inference, since it decides the species. 



Eupomatus heteroceros, Grube. 



Grube, 'Verh. zool.-bot. Ges. Wien,' 1868, p. 639, Taf. 7, fig. 8. 



Locality : Several specimens from South-west Cheval and East Cheval, 8 fathoms. 



Tube round, except flattened surface of attachment, doubled upon itself, U-shaped, 

 or slightly convoluted and faintly ridged ; it shows coarse growth rings and is 

 overgrown with Bryozoa and pearl-oyster byssus. Thoracic uncini sexdentate. The 

 opercular disc carries a crown of seven hooks turned inwards, of which one is larger 

 and plain, the others equal among themselves and each provided with a pair of 

 accessory lateral hamuli, and an inwardly directed basal process. The lateral hamuli 

 are inserted lower down the shafts of the coronal hooks than in Grube's figures, and 

 the basal hamules appear less upturned. The latter can hardly be seen without 

 bisecting the operculum. The bayonet seta? of the first fascicle have bicuspidate 

 processes as figured by Grube. The uniserial thoracic uncini, not observed by Grube, 

 show five and six teeth, rarely seven. The marginal denticulations of the opercular 

 disc end in rounded spatulate expansions. 



The collection contains many examples of this species. In one series of seven 

 individuals from the South-west Cheval, 13th November, 1902, one specimen has 

 eight hamuliferous hooks on the operculum, in addition to the great hook instead of 



* Compare E. albiceps. 



2 s 



