﻿418 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 102 



to subpyrif orm ; retractor muscles attached to body wall a little less 

 to a little more than five-sixths total length from mouth; fixing muscle 

 F^ attached to ascending intestine behind F^ mth sometimes a sub- 

 sidiary branch to postesophagus ; Polian tubules more numerous. 

 Tentacles six, the two dorsals shorter than the others. Length up- 

 ward of 170 mm. 



Description. — It is difficult to state any external characters by 

 which specimens of dyscritum may be distinguished easily from 

 zostericolum, other than the shorter trunk. The body is peppered 

 with small, rather uniform, circular, convex, hght-brown or dark- 

 brown glands, 0.08 to 0.1 mm. in diameter, and situated about 0.5 

 mm. apart on body and 0.25 mm. on introvert. They are thus larger 

 than in zostericolum and the border of each gland is more sharply 

 defined. On the introvert they lengthen to low papilliform and 

 extend to the red collar, which is smooth. In a zone around the anus 

 the glands are usually larger and more widely spaced than on the 

 body, and the roughly rectangular areas of the cuticle are more 

 obvious. The same thing occurs in many specimens of zostericolum, 

 especially when they are small. 



The distance between the origin of the retractors and the posterior 

 extremity is much shorter than in D. zostericolum, being from one-fifth 

 to a little less than one-sixth the total length. In zosteiicolum the 

 distance is one-fourth to one-third the total body length. The 

 spindle muscle is strong, attached dorsal to anus and is fused to the 

 wall of the rectum as far as coecum, beyond which it anchors ascending 

 spiral of intestine, by muscular strands in the generic manner. The 

 attachment of the fixing muscles F^ and F^ is normally as in zosterico- 

 lum; F^ is not attached to the postesophageal gut but to the intestine 

 at the top of the spiral, normally behind F^ (fig. 87, B). In one 

 variation (Crescent City) F^ is attached to the postesophageal intestine 

 and from its opposite side continued to the ascending gut (fig. 87, C). 

 Other variations are shown in fig. 87, D and E. FMs occasionally 

 absent (fig. 87, C), or it moves backward on the gut (fig. 87, D), while 

 F2 may be double (fig. 87, D, E). Rarely, F^ and F^ are absent 

 (specimen 170 mm. long. Crescent City). 



The alimentary canal shows no outstanding peculiarity. The 

 spiral contains 15 or 16 double coils (30 to 32 smgle). The nephridia 

 are shorter than in zostericolum. They vary from the maximum as 

 shown in plate 34, figure 1, to about one-half that length. 



The contractile vessel has more numerous Polian tubules than in 

 zostericolum, they branch at the base as well as distally, and they are 

 more crowded at the distal end of the contractile vessel than in 

 zostericolum. Plate 30, figure 3, shows a typical example. 



Color in life: Body dark olive-green, greenish yellow, or sepia, 

 sometimes stained blackish by the mud in which they live; introvert 



