248 ZOOPHYTA ASCIDIOIDA. 



34. Membranipora. Polypidom membranous ; the cells distinct, 

 membranous with an ossified rim to the aperture which is patulous. 



Family V. ESCHARIDiE. 

 Polypidoms calcareous^ membrano-calcareous or membranous, 

 very variable in form, composed of cells usually disposed in 

 quincunx ; the cells oblong, pentagonal or hexagonal, conjunct, 

 immersed or horizontal to the plane of axis, icith a subterminal 

 or lateral aperture usually covered with an operculum. 



35. Flustra. Cells quadrangular or hexagonal, on one or two 

 planes, forming mat-like expansions, free and foliaceous or incrusting. 



36. Cellularia. Cells oblong with a terminal aperture, in two 

 sublaternate rows on a single plane, forming a dichotomously divided 

 narrow subcalcareous polypidom. 



37. Acamarchis. Cells oblong with a wide lateral aperture, in 

 two subalternate rows, forming a dichotomous confervoid polypidom. 



38. Farcimia. Cells rhomboidal, immersed ; the polypidom di- 

 chotomous, with jointed cylindrical branches. 



39. Retepora. Cells immersed, quincuncial, on the upper side 

 of a frondescent, netted, calcareous polypidom. 



40. Eschara. Cells immersed, quincuncial, in a double layer 

 placed back to back like the cells in honey-comb, forming a frondes- 

 cent membrano-calcareous polypidom. 



Family VI. ALCYONIDUL.^. 

 Polypidoms sponge-like, fleshy, polymorpihous ; the cells irre- 

 gular in disposition, immersed and concealed, loith a contractile 

 non-operculate aperture. 



41. Alcyonidium. Cells immersed, irregular, with a contractile 

 aperture, forming a fleshy lobed polypidom. 



42. Cliona. Cells amorphous, perforated in a sponge-like polypi- 

 dom strengthened with siliceous spicula. 



** Lacustkine. (Tentacula in the form of a horse-shoe.) 

 Polypiaria hippocrepia, P. Gervais- 



Family VII. LIMNIADES. 



Polypidoms fleshy or spongy or corneous, polymorphous, the 

 polypes placed in tabes tvith angular or round orifices, closed 

 lohen the animals recede. 



43. Cristatklla. Polypidom fleshy or sponge-like, massive. 



44. Plumatella. Polypidom horny, fistular, confervoid. 



