262 bi'lletin: museum of comparative zoology. 



series are expanded above their bases into short broad plates shaped some- 

 what Hke the liead of an adze with edge of blade c<!tad and narrowed end 

 mesad, the plates lying contiguously as a pavement or with edges more com- 

 monly overlapping, between bases of the other two series of paleoli. They 

 nimiber about twenty-two in each series. The opercular lobes together as a 

 whole are long, strongly expanded distally, in a trumpet-form greatly exceed- 

 ing the rest of the body in diameter. The parathoracic notopodial paleoli 

 are elongate, thin blades with sides nearly parallel to near tip where they 

 expand a little clavately and then narrow abruptly to an acute apex. The 

 body as a whole is very slender, in all cases with a segment at anterior end of 

 abdomen characteristically globularly thickened. 



The greatest thickness of thorax about 1.8 mm., M'hile the width 

 across end of the opercular lobes is up to 1.6 mm. 



Locality. — Calif.: San P'rancisco (A. Agassiz). Numerous speci- 

 mens. 



Type.— M. C. Z. 2,132. Paratypes.— 'Sl .C. Z. 482. 



25. Idajstthyrsus ornament atus, sp. nov. 



Plate 3, fig. 2-5. 



General color brown. On each side of operculum at about middle of length 

 a large, dark, almost black, spot with a line-like dorsal prolongation to the 

 dorsal furrow. Also a narrow deep colored stripe below the outer series of 

 paleoli on each side. Achaetous caudal region dark anteriorly. Outer paleoli 

 yellow, the inner ones darker, bronze colored. Outer paleoli pinnately 

 branched and the inner ones slender and wholly smooth. Outer paleoli in a 

 series extending around anterior end of inner series, thirty-six in number. 

 Inner paleoU eleven or twelve in each series. Area outlined by the two series 

 on each side very narrow. Papillae below outer paleoli short, conical, well 

 separated, fifteen on each side of which the anterior three are longer than the 

 others. Two pairs of nuchal hooks present in the type. Second setigerous 

 somite with three cirri above setigerous papilla on each side; of these the 

 most dorsal is largest and corresponds in form, size, and position to the 

 branchiae of the succeeding somites; the two below this much shorter, stout, 

 and rounded. The dorsal thoracic paleoli nine or ten in nimiber; not at all 

 clavately widened distad, the plates rather narrow with sides parallel to 

 acutely attenuated distal region, this acuminate region rather long with the 

 narrowing gradual and even, the species in the form of the paleoli being readily 

 distinguishable from /. johnstoni (Mcintosh) and /. armata (Kinberg) which it 

 resembles in the form of the opercular paleoli. Ventral thoracic setae very 

 slender. Uncini elongate and slender, much as in /. regina Chamberlin but 



