CENOTHRIX MUTANS. 331 



The pygidium has a highly peculiar form in the type which may possibly 

 be the result of regeneration. It is abruptly ver>^ much narrower than the 

 preceding somite. It presents a basal di\'ision, which has a convex surface 

 and narrows caudad and may represent a distinct somite, and a more slender, 

 cylindrical, distal division, which bears at its distal end two stout cirri, which are 

 contiguous at the base, are very short, in length less than the diameter of the 

 adjoining region of the pygidium, and are bifid at the distal end. 



The parapodia are strictly lateral and about equidistant from dorsal and 

 ventral lines. All are small, the most anterior ones being smallest, while the 

 caudal ones are not reduced. All are short and cylindrical with no distinct 

 presetal Up but with a very conspicuous postsetal finger-like process which is 

 cylindrical, or rather slightly conical, and rounded at the tip. The postsetal 

 process extends ectocaudad. It is of the same form and proportionate size 

 throughout the body. The notopodium is represented by a slight tubercle 

 above at the base of the neuropodium. No cirri are evident. No branchiae 

 at all. (Plate 61, fig. 9). 



The nem-opodial acicula are normally two in number. They are stout at 

 base and rapidly narrow to an acute fine tip. Each is slightly curved, with the 

 concavity ventrad. (Plate 61, fig. 5) The more dorsal aciculum is pale yellow 

 excepting the slender tip, which is colorless. The ventral aciculum is pale 

 yellow proximally, but toward the tip becomes much darker brown, the tip 

 colorless, as in the other. The setae are all simple and are of two types, capillary 

 ones and stout spines. Of these the former are colorless, the latter yellowish. 

 The capillary setae are all of the usual bilimbate type and all are bent a httle 

 above the proximal end of the limbate region, some abruptly so, or geniculate. 

 In the latter type a limbus, as seen in side view, is proximally broad, narrowing 

 gradually distad, and fading out at base of the long slender tip; at the base 

 along the convex free margin is a series of projecting teeth or scales, the edge 

 elsewhere smooth. (Plate 62, fig. 1). In the other type the limbi are narrower 

 and lack the scales, or have these but obscurely indicated and not projecting at 

 all as teeth. (Plate 61, fig. 8). In the middle region a parapodium has ordi- 

 narily but one of the more strongly curved, scale-bearing, limbate setae, and 

 only two of the other, smooth Umbate, tyi^e. Of the stout spines, never more 

 than one seem to be present in any parapodium. These are yellow in color 

 throughout and are stout and curved. Each of uniforai diameter excepting at 

 the distal end, where it narrows conicaUy and is wholly without terminal teeth 

 or subapical spm- or process; the membranous guards are very unsymmetrically 



