IDANTHYRSUS CIIETUS. 485 



Idanthyrsus Kinberg. 



Annulata nova, 1866, p. 349. 



PallaMu QuATREFAGKS, Hist. nut. anneles, 1805, 2, p. 322. 



Idanthyrsus cretus, sp. nov.^ 

 Plate 75, fig. 8-15. 



The general color is a dilute yellowish. The branchiae are tinged with 

 purplish, as is also the under surface of the opercular lobes. The cirri of the 

 slender posterior region of the body are solid purple. The opercular paleae 

 are golden yellow, some darker, more orange tinged, the thoracic ones paler 

 and the other setae of the thoracic and abdominal regions unpigmented, in 

 groups appearing white. 



The total length, inclusive of the opercular folds, is nearly 20 mm., of which 

 the slender faecal tube comprises 4 mm. The width across the anterior end of the 

 abdomen is 2.7 mm. The width across the opercular lobes, exclusive of the 

 palea, is 4 mm. Forty-two setigerous somites, or very near that number, 

 are present. 



The mouth is a triangular opening bordered on each side by a longitudinal 

 palpal fold which is high and thin. 



The opercular folds diverge conspicuously cephaloectad. Each fold pre- 

 sents a distal surface limited by paleae, which is narrowly elliptic in outline or 

 more pointed at one end. There are two rows of paleae, an inner and an outer, 

 the two series almost touching at the ends. The paleae of the inner series are 

 thirteen to seventeen in number; they are all smooth and not very stout, nar- 

 rowing from base to an acute apex and distally weakly curved. They increase 

 in length and stoutness from the upper (mesal in type) to the ventral (c^ctal) end, 

 those toward the latter end also being much closer together. They are longi- 

 tudinally fibrillate and closely, finely cross-striate. (Plate 75, fig. 11). The 

 paleae of the outer series are sixteen to twenty in number. Thej^ are longer 

 and much more conspicuous than those of the inner series and similarly increase 

 in length and closeness toward the outer (ventral) end. They are all strongly 

 plumose, the branches long and extending farther proximad on one side than 

 on the other. Each shaft is acutely pointed and is curved at the tip; it is in 

 part finely transversely lined. (Plate 75, fig. 12). At the upper end of the 

 series of paleae on each fold there is a single stout, very dark reddish, heavier 

 nuchal hook, the distal portion of which is bent directly transversely and is not 



^ cernere, to separate. 



