248 
ZOOPHYTA ASCIDIOIDA. 
34. Membranipora. Polypidom membranous ; the cells distinct, 
membranous with an ossified rim to the aperture which is patulous. 
Family V. ESCH ARIDvE. 
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 , with a subterminal 
or lateral aperture usually covered ivith 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. ALCYONIDULiE. 
Polypidoms sponge dike, fleshy , polymorphous ; the cells irre- 
qular in disposition , immersed and concealed , with 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. 
** Lacustrine. (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 tubes ivith angular or round orifices , closed 
when the animals recede. 
43 Cristatella. Polypidom fleshy or sponge-like, massive. 
44. Plumatella. Polypidom horny, fistular, confervoid. 
