COPHONCHUS, ISONEMELLA 329 



ing first inward, then directly forward. It is about one-third as long as the cor- 

 responding body-diameter. Its outlet is opposite the middle of the spicula. 

 There appear to be some obscure papillae on the tail, evidenced by almost imper- 

 ceptible ventral elevations. Mention may be made of one of these near the 

 beginning of the middle third, and another near the beginning of the posterior 

 third. Spicula slender, uniform, acute, one and one-half times as long as the 

 tail, and five to six times as long as the anal body-diameter. Their proximal 

 ends are cephalated by expansion. They are accompanied, both in front and 

 behind, at their distal extremities, by accessory pieces two-thirds as long as the 

 anal body-diameter. The ejaculatory duct is one-fourth as wide as the body, 

 and extends forward to near the middle of the body, where it joins the testes. 



Habitat: Shoal in Kingston Harbor, Jamaica, in about one foot of water. This 

 genus bears a very considerable resemblance to Digitonchus. Fig. 108, p. 328. 



109. Isonemella acuta n. sp. ' 7 / Body-wall thick 



and muscular; in the middle of the single specimen seen it takes up about three- 

 fifths of the radius. There are a few exceedingly minute setae to be seen on 

 the tail; otherwise than these, and those shown in the illustration, no others are 

 known. There appear to be three lips, but they are so small and so thoroughly 

 amalgamated that it is very difficult to decide on their structure, and it is possible 

 that there is no division of the margin of the mouth into lips. The mouth opening 

 is nearly as wide as the front end of the head. Between the thin lips there is a 

 very short vestibule, whose limits are marked by the presence of an internal 

 refractive structure on the inner wall of the pharynx very near the margin of the 

 lips. It is impossible to say from the observations so far made whether this 

 refractive marking is a circular affair or whether it is dis- setl/ffl 

 continuous and represents special thickenings on the inner ^ 

 surface of the three components of the lip-region. The 

 result of this thickening is a sudden, but very slight nar- am P" 

 rowing of the vestibule. The very short vestibule, there- DC . 

 fore, begins nearly as wide as the front of the head, widens ^ 

 out posteriorly and then soon suddenly narrows to the 

 beginning of the pharynx proper. At its base this lat- *" 

 ter tapers to join the lumen of the oesophagus. At 

 first sight it appears that, with the exception of the above- 

 mentioned, excessively minute, cutinized processes at the 

 base of the vestibule, the pharynx does not present any 

 feature suggestive of a particular armature, but there is spn x750 



nevertheless a minute, forward-pointing ventral (?) onchium of small size. The 

 walls of the pharynx, though distinctly outlined by the refractive nature of 

 the cuticle, are very thin throughout. The lip-region stains more strongly 

 than any of the succeeding tissues of the head, or of the anterior part of the 

 neck. All that portion of the lip-region in front of the middle of the pharynx 

 takes part in this staining, and the posterior contour of the stained portion 

 extends outward and backward from the front part of the pharynx. Behind 

 this stained portion, indicated in the illustration, there are two elongated "cavi- 

 ties," beginning opposite the middle of the pharynx and ending a little behind 

 the eye-spots, one dorsal and one ventral, and the outer contour of the head 

 opposite these "cavities" is very slightly elevated, in the single specimen so far 

 examined. When viewed in profile these "cavities" have a size and contour 



