556 MIMOSELLIDiE. 



vation. When the polypide^ however, issues from its 

 dwelling, the membranous wall is drawn inwards, a de- 

 pression or cleft is distinctly visible, and the cell appears 

 distorted ; the solid part is somewhat boat-shaped, form- 

 ing a kind of shield. 



I have not been able to detect any special arrangement 

 of muscles connected with the remarkable movements of 

 the zooecia ; and from their character, and the fact that 

 they are coincident with the expansion and retraction of 

 the polypide, I should certainly regard them as dependent 

 on these changes, were it not that I have, on more than 

 one occasion, seen cells from which the polypide had 

 disappeared move backwards and forwards. 



The folded cells open slowly ; and there is an occasional 

 pause before they are thrown fully back. They begin to 

 close (as it seems) not when the polypide merely retreats, 

 but when it draws itself down to the very bottom of its 

 cell. Then they instantly begin to fold up, moving 

 slowly at first, but, when they have fairly swung round to 

 the front side of the stem, closing rapidly with a kind of 

 jerk. A hollow at the base of the cells fits over a tubular 

 projection on the stem; and upon this they sway back- 

 wards and forwards. 



The polypide is small, with a short and slender stomach, 

 and is destitute of a gizzard. 



MiMOSELLA GRACILIS, Hincks. 

 Plate LXXIV. figs. 1-0, aud Woodcuts, figs. 27 & 34. 



MiMOSELLA GRACILIS, Hiiicks, Aiiii. N. H. ser. 2, viii. 359, pi. xiv. figs. 5-8 ; 

 xi. 184 ; Dev. Cat., Ann. N. H. ser. 3, ix. 472 (58, sep.), 

 pi. xvi. fig. 1 : Heller, Bryoz. Ad. M. 52, pi. Ti. figs. 1, 2. 



Valkeria cubcuta, Couch, Com. Faun. iii. 9(), pi. xvii. fig. 3. 



Zoarium erect, confervoid, of a light horn-colour, consist- 

 ing of slender, jointed, tapering stems, much and ir- 



