igii.] N. Annandale : A Rhizocephalon from fresh water. 3 



mantle is thin and smooth but is well provided with slender 

 circular muscle-fibres. The two ovaries are distinct, but a testis 

 has not been detected, 



Sesarmaxenos uionticota, sp. nov. 



In the only known specimen of this species the body bears a 

 close superficial resemblance to a slug with two tentacles partially 

 withdrawn, their position being occupied by the papillae on which 

 the orifices are situated. This end of the body is truncate, the 

 orifices being separated by a distance a little greater than \ of the 

 total length. The other end is pointed, the whole body being 

 sinuous. The colour, after some years in spirit, has probably 

 faded, but the surface has a purplish tinge which is most distinct 

 at the two ends and round a small pit on the exposed surface {i.e., 

 exposed when the abdomen of the host is removed) not very far 

 from the pointed end. This pit possibly indicates the position of 

 the nerve-ganglion. The slit-like orifices are parallel to the 



Fig. 



-Advanced larva from brood-pouch of S. monticola, x 450 



longitudinal axis of the host. The muscle surrounding them is 

 powerful, its fibres crossing one another obliqueh^ in various direc- 

 tions and finally constituting two distinct strands which run along 

 the exposed surface in a somewhat divergent course. 



The larvae in the brood-pouch apparently represent two dis- 

 tinct instars, both of the cjqjrid type but one larger and better 

 developed than the other. Those of the more advanced form 

 measure about 0*3 mm. in length and 0'i49 mm. in greatest depth, 

 the whole animal being nearly semicircular in outline. Both ends of 

 the shell are narrowly rounded or somewhat truncate, and the ven- 

 tral margin is slightl}^ sinuous. The abdomen is minute but dis- 

 tinctly segmented. At its tip it bears a pair of short bristles. The 

 six cirri are well developed, each bearing a bunch of bristles directed 

 forwards in a slanting direction. The whole animal is strongly 

 compressed and the shell is very thin and transparent. The eye 

 is situated at about -j of the distance between the anterior and 

 posterior ends of the shell. The smaller instar only dift'ers in size 



