Mr. P. H. Gosse on a new species of Leech. 277 



Fig. 4. Lenticulites complanatus : a, natural size of this Foraminiferous 

 shell ; b, a section magnified, showing the cells : — large rocky 

 masses of this fossil occur in the yellow sand associated with the 

 Urchins of that deposit. 



XXV. — On Monopus medusicola_, a species of Leech. 

 By Philip Henry Gosse, A.L.S. 



[With a Plate.] 



In my ' Devonshire Coast ' (p. 359) I have mentioned the occur- 

 rence of a small Leech parasitic on the Medusa, Wiilsia stellata. 

 As I have not been able to assign it to any recognized genus 

 of the Hirudinidce, I will here repeat the characters, give a figure 

 of it, and appropriate to it a name. Though the note and the 

 drawing taken of it at the time, are not so detailed as I could 

 have wished them to be, yet as I can answer for their accuracy 

 so far as they go, they will at least serve to identify the form, 

 should it occur again. 



MoNOPUs (mihi). 



Body soft, subcylindrical, depressed ; anterior sucker imper- 

 fect j posterior a circular disk, at the extremity of a short thick 

 truncate column, distant one-third of the total length from the 

 anal extremity, on the ventral side. Anterior extremity obtuse; 

 posterior briefly attenuate. Eyes eight, set around the frontal 

 margin of the anterior disk. Intestinal canal straight, simple ; 

 anus terminal. 



Monopus medusicola (mihi). 



Less than 1 line in length ; pellucid : eyes hyaline : parasitic 

 on Medusae. 



The ovary was ample, and contained a number of clear, glo- 

 bular, highly refractile ova, variously grouped, in the posterior 

 moiety of the abdomen. Close-set transverse annuli surrounded 

 the anterior portion. The intestinal canal had two fusiform 

 swellings, and was enveloped near the oesophagus with opake 

 cloudy matter. 



The generic name was suggested by the foot-like appearance 

 of the posterior sucker. 



EXPLANATION OF PLATE VIII. B. 



Fig. a. represents Monopus medusicola, ventral surface. 

 Fig. b. the same, laterally. 



68 Huntingdon Street, Barnsbury Park, March 5, 1855. 



