very small. Tail scarcely exceeding in length '/3 of the anterior division; anterior 

 part of genital segment considerably expanded. Caudal rami comparatively short, 

 being only slightly longer than they are broad, outermost seta somewhat remote 

 from the apex, inner mediate one a little longer than the tail. Anterior antennae 

 about half the length of the cephalic segment, and composed of 9 joints, 2nd 

 joint the longest; terminal joint somewhat exceeding in length the 2 preceding 

 joints combined. Posterior antennae with the terminal joint about as long as 

 the preceding one; middle apical seta rather slender, the other 2 short. Siphon 

 comparatively strong and gradually tapered distally, extending somewhat beyond 

 the limits of the cephalic segment. Maxillee with the inner lobe only slightly 

 longer than the outer and rather narrow, apical seta scarcely as long as the 

 lobe; apical setse of outer lobe rather slender. Anterior maxillipeds with the 

 dactylus very slender and elongated, terminating in a short, slightly curved claw, 

 and armed at some distance from this claw with a small secondary spine. 

 Posterior maxillipeds normal. Natatory legs with the spines of the outer ramus 

 comparatively short, 2nd basal joint in 2nd 4th pairs angularly produced inside; 

 4th pair with the outer ramus fully as large as in the 2 preceding pairs and 

 armed in a similar manner; of an inner ramus not the slightest rudiment present. 

 Ovisacs globular in form. 



Male considerably smaller than female, and having the anterior division 

 of the body less broad. Genital segment greatly swollen, to receive the 2 globular 

 spermatophores. Anterior antennae composed of 11 joints, and distinctly hinged, 

 the last 2 joints forming together a movable part, which admits of being bent 

 upon the adjoining part of the antenna; 8th joint somewhat dilated, and armed 

 in the middle of the anterior edge with a short spine. 



Colour of female generally pale yellowish grey, with a few small reddish 

 spots on the cephalic segment; intestine and its distinctly lobular coeca of a 

 darker yellow hue. 



Length of adult female amounting to 1.45 mm., of male to 1.10 mm. 



Remarks. This form was described by Thorell from a solitary female 

 specimen taken by Lilljeborg in the open sea, and was supposed by that author 

 to be, like Ascomyzon Littjeborgi, an internal parasite of Ascidise. It has sub- 

 sequently been recorded in both sexes by several other authors, though in some 

 cases it appears somewhat doubtful, whether the descriptions in reality refer to 

 the present species or to some other nearly-allied form. The form at first 

 recorded by Giesbrecht from the Bay of Naples as Gallopontius rotundus has 

 subsequently been identified by that author with the present species. From the 



