FREE-LIVING FRESH-WATER NEMATODES 77 



nerve-ring is in front of it. The blind end of the posterior testicle lies just 

 in front of the anterior supplementary organ. 



Habitat: Mud, Potomac River. Sublimate to balsam. 



TYLENCHUS, Bastian, 1865. 



60 



24. Tylenchus symmetries, n.sp. 2 -7 108 17. -49- 90.2 mm 



i-4 2.8 3.3 3.8 2.7 



The moderately thick layers of the transparent, colorless, naked cuticle 

 are traversed by fine plain transverse striae, which are not further resolvable. 

 There are two wings on the lateral fields, removed from each other a dis- 

 tance about equal to one-fourth to one-fifth the body diameter. The space 

 between these wings is very faintly marked with longitudinal lines, of which 

 two near the middle are more prominent than the others. The wings them- 

 selves bear traces of transverse striation. These wings begin near the 

 middle of the neck and end on the tail. The conoid neck becomes convex- 

 conoid toward the somewhat rounded head, which is not set off, or at least 

 only by an almost imperceptible constriction a short distance behind the lip 

 region. There are no distinct lips. What appear to be the faintest possible 

 traces of papillae may be seen on the lips, but these do not disturb the rounded 

 contour of the head. Were it not for the innervations it would be prac- 

 tically impossible to see them. The pharynx is tubular and just wide enough 

 to make a passage for the spear. This latter is slender, nearly one and one- 

 half times as long as the base of the head, and has a three-bulbed base about 

 one-fifth to one-fourth as wide as the corresponding portion of the head. 

 Near the middle the spear is closely surrounded by a rather inconspicuous 

 guiding-ring or cylinder, about one-fourth as long as the spear. At its 

 widest part, namely, in the proximal half, the diameter of the spear is less 

 than the width of two of the adjacent annules of the cuticle. The oesophagus 

 begins as a tube about one-third as wide as the base of the head, and con- 

 tinues to have this diameter until it expands to form the ellipsoidal or pro- 

 late median bulb. This latter is about three-fifths to two-thirds as wide as 

 the middle of the neck, and contains a distinct ellipsoidal valvular apparatus 

 about one-fifth as wide as the bulb itself. Behind the median bulb the 

 oesophagus is smaller than elsewhere. For a distance equal to twice the 

 width of the neck it has a width only about one-eighth to one-sixth 

 as great as that of the corresponding portion of the neck. There- 

 after, it expands to form the elongated-pyriform non-muscular cardiac swell- 

 ing, which is half as wide as the base of the neck, and contains a rather 

 conspicuous nucleus. The lining of the oesophagus is a fairly distinct feature 

 in its anterior part; but posteriorly it is much less distinct, and is very diffi- 

 cult to observe in the cardiac swelling. The intestine, which is separated 

 from the oesophagus by an indistinct constriction, becomes at once fully two- 

 thirds as wide as the body. Its cells are packed with large granules of some- 

 what variable size, the largest of which have a diameter about one-eighth as 

 great as that of the body, the smallest being considerably smaller. These 



