a General History of the Marine Polyzoa. 161 



be best understood by referring to the figure. The lamina or 

 plate which protects it is hollowed out in front. This plate 

 passes down for a considerable distance into the interior of 

 the cell ; immediately within it is placed the semicircular 

 frame on which the oral valve works, which fits close on to 

 the inner surface of the lamina. The flattened, shield-like 

 ovicell is another striking feature. 



The structure of the zooecium in this species is so remark- 

 able that I cannot hesitate to refer it to a new genus. Busk, 

 in his ' Catalogue,' describes an Eschara {E. gigantea), from 

 South Patagonia, which bears some slight general resem- 

 blance to the present species ; but neither the diagnosis nor 

 the figure represents the essential peculiarities of A. crassum. 



EXPLANATION OF THE PLATES. 

 Plate VIII. 



JFig. 1. Membranipora cervicorms, MacGillivray, to show the structure 

 of the zooecium. The forked spines omitted, except in the case 

 of a single cell, and only the fixed tubular base represented. 



Fiff. 2. Membranipora (C'alescha)-a) denticulata, MacGillivray. In this 

 figure the membranous wall, which closes in the entire front of 

 the cell, is omitted, so as to display the calcareous lamina and 

 the offset from its upper margin, which together form an inner 

 covering over a considerable portion of the area. The semi- 

 circular oral valve at the top of the area must be understood to 

 belong to the absent membranous front wall. 



^^9- 3. Meinbranipora setigera, n. sp. 



■^''9- 4. Membranipora belMa (normal form), n. sp. 4 a. Ditto, var. bi- 

 cornis. 4 6. Ditto, var. multicornis. 



Fig. 5. Membranipora terrifica, n. sp. 



Fig. 6. Membranipora rubida, n. sp. 



Fig. 7. Diachoris bilaminata, n. sp. 7 a. Zooecium with avicularium. 



Plate IX. 



Fig. 1. Membranipora bicolor, n. sp. 



Fig. 2. Schizoporella linearis, Hassall. Variety with avicularia at the 



top of the cell and on each side of the ooecium. 

 Fig. 3. Schizoporella linearis, var. quincuncialis. 

 Fig. 4. Metnbranipora patula, n. sp. 

 Fig. 5. Smittia nitida, Verrill. [This figure represents a very irregular 



group of cells.] 5 a. Zooecium with ovicell. 

 Fig. 6. Schizoporella argentea, n. sp. 6 a. Single zooecium. 



Plate X. 



Fig. 1. Metnbranipora coronata, n. sp. 



Fig. 2. Membt-anipora permunita, n. sp. 



Fig. 8. Membranipora cervicoi-nis, MacGillivray, var. 3 a. Ooecium. 



Fig, 4. Vincularia abi/ssicola, Smitt. From an incrusting colony. 



Fig. 5. Epicatdidium ^pidchrum, n. sp. 5 a. A single triplet of celh. 



Fig. 6. Aspidostoma crassum, n. sp. Showing a group of cells from the 



younger and older portions of the colony. 6 a. Fragment of the 



zoarium, nat. size. 



