330 THE ANNELIDA POLYCHAETA. 



Cenothrix mutans, sp. nov.^ 

 Plate 61, fig. 1-9; Plate 62, fig. 1. 



The type as preserved is throughout grey, in part of a weak flesh color or 

 delicate rose tinge. 



The body is elongated and slender, terete. It is tapered at the ends, but 

 elsewhere is nearly of uniform diameter, being but slightly thicker anteriorly 

 than posteriorly. The length is approximately 107 nun., the maximum width, 

 exclusive of parapodia, 1.6 nun. The number of somites is about 280, the 

 coiled condition of the type rendering exact counting difficult. 



The prostomium is ovate, clearly longer than wide, with the anterior end 

 narrowly rounded. A little flattened dorsoventrally. Surface very smooth. 

 On the ventral surface there is a weak median longitudinal furrow which does 

 not reach either end and is bounded laterally by shght, broad ridges, which are 

 confluent caudally in front of the mouth. Palpi not distinct. Eyes none. 

 (Plate 61, fig. 4). 



The peristomium is set off from the prostomium by a deep constriction. It 

 is much shorter than the prostomium, but is wider. It and the second somite 

 together are about two thirds as long as the prostomium. The outline in pass- 

 ing from prostomium to peristomium is abruptly changed, but from the peri- 

 stomium caudad it is evenly continuous. Both peristomium and the second 

 somite are apodous. The peristomium is much longer than the second somite 

 laterally, as it there curves conspicuously forwards, but is slightly incurved at 

 the middle above. On the ventral side it is but little longer than the second 

 somite and is crossed longitudinally by a few distinct sulci. The second somite 

 is of nearly uniform length above and below, and is throughout deeply separated 

 from the peristomium. (Plate 61, fig. 4). 



The succeeding somites are all simple and regular, and are smooth except- 

 ing for a few weak, often somewhat oblique, sulci crossing the somites longi- 

 tudinally and evident only under the microscope. The cuticle has the usual 

 shining and iridescent appearance. A few sulci may be more distinct in the 

 middle and posterior regions. Each parapodium is inserted in a sharply marked 

 furrow crossing the somite longitudinally. The somites increase in length to 

 about the seventeenth, after which the length is uniform, or nearly so, to the caudal 

 end of the body. The somites, more particularly in the anterior region, curve 

 forwards on each side just in front of the parapodium. 



' mutare, to change. 



