66 NORTH AMERICAN 



anus as the terminus is behind it. The testes are broad and some parts appear 

 to fill up the main portion of the body cavity. 



Habitat: Sand bar off Plummer's Island, Potomac River. Subli- 

 mate to balsam. 



ONCHOLAIMELLUS, de Man, 1886. 

 Fig. 21, Plate VII. 



53 

 o 85 18 -M- QI 



18. Oncholaimellus heterurus, n.sp. 1.2 mm. 



.8 1.5 1.8 1.8 1.4 



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

 seem to be destitute of markings of any kind. If there are any striations 

 they must be exceedingly minute. The conoid neck becomes a little convex- 

 conoid toward the head, which is subtruncated, and has a lip region almost 

 imperceptibly expanded. There are ten long, curved, tapering, cephalic 

 setae, located a trifle in front of the middle of the pharynx, two lateral, and 

 eight submedian. The members of the submedian pairs are placed one in 

 front of the other, the hinder members being only about two-thirds as long 

 as the forward members. It is the forward members that are in the same 

 circlet with the lateral setae. These latter are about as long as the longest 

 submedian setae. The bases of the lips are nearly as thick as the wall of 

 the head, but they gradually become quite thin, though the flaps are not so 

 marked as they usually are in Oncholaimus. There are six lips, and each 

 bears on its anterior surface, near the margin of the head, a somewhat out- 

 ward pointing, minute, innervated papilla, which does not very markedly in- 

 terfere with the contour of the front of the head. The somewhat cylindroid 

 pharynx is about twice as long as the front of the head is wide, and the 

 average diameter of the cavity is a little more than one-third of its length. 

 At the middle the pharynx is about half as wide as the corresponding por- 

 tion of the head. Its walls are fairly well chitinized, and appear to be des- 

 titute of onchi. The description is derived from a single specimen, in which 

 the mouth is filled with detritus, and it is possible that very minute teeth 

 might have escaped observation, but this does not seem at all probable. 

 The bottom of the pharynx where it is set on the end of the oesophagus, is 

 in the shape of a broad, shallow, hollow cone. At a distance from the 

 anterior extremity twice as great as the length of the pharynx the amphids 

 are seen. These are somewhat elongated, roughly ovate in contour, and 

 more distinctly marked anteriorly than posteriorly. The anterior border is 

 a curved, chitinous structure about one-third as wide as the corresponding 

 portion of the head. Slightly behind the anterior border the amphid has its 

 greatest diameter. It is about as long as the corresponding radius of the 

 head, and is extended backward by an apparently tubular structure, which 

 soon becomes indefinite. Viewed dorso-ventrally the amphids appear like 

 rather deep invaginations of the cuticle, and each occupies fully half of the 



