THOONCHUS 



311 



"striping" whose presence is indicated mainly by the arrangement of these 

 minute yellowish granules. The stout tail diminishes rapidly from the posterior 

 lip of the anus, so that at the middle it has a diameter about two-thirds as great 

 as at the base; thence onward it is nearly cylindroid to the rounded terminus. 

 The caudal glands are located in a tandem series considerably in front of the 

 anus; the hindermost being about four times as far from the anus as the termi- 

 nus. The two anterior glands are close together and are nearly as far in front 

 of the hindermost as this latter is in front of the anus. From the elevated vulva, 

 the vagina extends inward half way across the body. The ovaries reach about 

 one-third the distance back to the vulva in specimens that contain three eggs 

 in the uterus. Eggs elongated, about twice as long as the body is wide and about 

 one-third as wide as' long. Each of the twc uteri may contain three eggs at one 

 time. Tail of the male more strongly arcuate than that of his mate. Clavate 

 caudal glands about as long as the body is wide and about one-third as wide as 

 long, arranged some distance apart in a tandem series. When the body of the 

 male is closely coiled, the ventral surface toward the posterior end becomes 

 corrugated in a definite way for some distance in front of the anus, suggesting 

 that this area may be systematically innervated and serve the purpose of a ven- 

 tral series of about two dozen subequidistant supplementary organs. These 

 corrugations are apparently innervated, but no distinct corresponding breaks 

 or openings have been seen in the cuticle. On the ventral side at a distance 

 in front of the anus three times as great as the length of the tail, there is an 

 elevated supplementary organ in the form of a transverse ridge. This occurs 

 in the midst of the corrugations just described, at least, it appears that the 

 corrugations extend beyond it, although they are not quite so close together 

 or so marked in this region. This supplementary organ begins near the sub- 

 median lines and extends across the ventral region. Its internal structure has 

 not been satisfactorily elucidated. It appears probable that the cuticle on 



the ventral line ^ mSllIm(txt\setCph(JOi dd CBBBte^^^ *SE S* 



is interrupted, 

 but even this is 

 not clearly es- " 

 tablished. This 

 swelling has two 

 to three times 

 the width of the 

 corrugations and 

 occurs at the 

 same position on 

 three different 



male specimens, 



X750 



extn 



so there can be 



no doubt about its being a distinct supplementary structure. Opposite the 

 middle of the spicula, also, there is a pair of subventral supplementary papillae, 

 accompanied by slender subventral setae in the rear. There are a few short 

 delicate setae on the tail, especially on the submedian lines, but also in front of 

 the anus for some distance, where they are longer, more nearly the size of 

 those on the anterior extremity. About a dozen pairs of copulatory muscles 

 occur in the ventrally submedian region, in a space four to five times as long as 

 the tail. Testes relatively small. 



Habitat: Open-ocean beach-sand, South California. Bay City, Huntington 

 Beach U. S. A. Fig. 91. 



