_Lepralia pallasiana_ (Fig. 13) forms sub-circular vitreous patches on stones and shells; the cells are rather large, broadly oval, and with the front wall punctured with pores; the aperture is squarish and with a slight indentation on each side. [Illustration: Fig. 13. _Lepralia pallasiana_, incrusting a shell. A, natural size; B, cells magnified. ] _Lepralia foliacea_ forms a massive coral-like growth composed of thin contorted plates which fuse to form labyrinthine cavities, the plates being constructed of a double layer of cells back to back. A large specimen from the English Channel is exhibited in Case B, upright part. In _Lepralia_ the orifice and lid of the cell have a straight lower margin, but one large group, _Myriozoidæ_, is characterised by having a notch in the lower margin of the orifice, (Fig. 14, _Schizoporella unicornis_). [Sidenote: Case B 1.] In many of the Escharina, the front wall of the cell is produced into a stout process or mucro at the lower margin of the orifice (genus _Mucronella_), or, again, a collar or tube grows up round the primary orifice, thus giving rise to a secondary orifice (_Smittia_, _Porella_, etc., Case B 1). [Illustration: Fig. 14. _Schizoporella unicornis_, magnified. ] [Illustration: Fig. 15. _Retepora beaniana._ ] [Sidenote: Case B 1.] In the _Celleporidæ_, (Case B 1) the cells are typically pitcher-shaped and arranged vertically, and tend to be heaped up from the overcrowding. _Cellepora pumicosa_ forms thick pumice-like masses composed of succeeding layers of cells. The _Reteporidæ_ (Case B 1) form delicate stony networks. The reticulate fronds may be expanded out, or may form tubular or contorted growths (Fig. 15, _Retepora beaniana_). The beautiful _Retepora phœnicea_ from Torres Straits is of a rich purple colour. The _Adeonidæ_ form thick fenestrated plates which unite to form cavernous masses usually attached to rocks by a thick jointed stem. Several very fine examples from Port Phillip, Victoria, are exhibited in the upright part of Case B. [Sidenote: Case A 2.] The _Catenicellidæ_ are represented by a fine series of specimens from Australia. The colonies form dense clusters of finely beaded branches. The cells are arranged in single series, each cell being united to those above and below by a horny joint. The cells are usually urn-shaped with a triangular avicularium at each upper angle, and with the front surface variously sculptured with pores or bands (Fig. 16, _Catenicella ventricosa_). [Illustration: Fig. 16. _Catenicella ventricosa._ A, natural size; B, magnified. (After Busk.) ] Sub-order 2.—CTENOSTOMATA. [Sidenote: Case B 2, and A upright part.] The Ctenostomata are fleshy, horny, or membranous; never calcareous. When the tentacles of a polypide are retracted into the cell, they are protected above by a membranous comb-like frill. The cells either bud off from each other or arise as buds on a stolon or stem.