154 SPONGES 



substance round the chambers clear ; canal system eurypylous. Genera 

 Spongelia, Ndo.; Velinea, Vosrn.; Psammoclema, Marshall; Psammopemma, 

 Marshall. FAMILY 3. APLYSINIDAE, F.E.S. Fibres hollow, canal system 

 aphodaL Genera Aplysina, Ndo. (Fig. 40) ; Luffaria (Duch. et Mich.), 

 O.S. ; Verongia, Bwk. ; Thorecta, Ldf. 



ORDER 2. Dendroceratina ( = Hexaceratina, Ldf., pars). 



Spongin fibres dendritic, arising from a basal plate of spongin, and 

 not anastomosing. 



FAMILY 4. APLYSILLIDAE, Vosm. Canal system eurypylous, with 

 large elongated chambers ; in Darwinella, spicules of spongin. Genera 

 Aplyvilla, F.E.S. ; Darwinella, Miiller ; lanthella, Gray ; Dendrilla, Ldf. 

 (Here Hexadella, Tops., finds its nearest allies, and perhaps also 

 Halisarca, Duj.). 



KERATOSA (1 FORAMINIFERA) incerti sedis (HAECKEL, 1889 [8]). 



FAMILY AMMOCONIDAE. " Keratosa without spongin fibres. Pseudo- 

 skeleton composed of xenophya (or manifold foreign bodies), which are 

 disposed in the thin malthar plate of the porous tubular body. Canal 

 system tubular, developed on the Asconal type (similar to that of the 

 Asconidae)" Genera Ammolynthus, H. ; Ammosolenia, H. ; Ammo- 

 conia, H. ; Prophysema, H. FAMILY PSAMMINIDAE, Ldf. " Keratosa 

 without spongin fibres. Pseudo-skeleton composed of xenophya . . . 

 which are cemented together and enclosed by the transparent maltha. 

 Canal system vesicular, developed on the Leuconal type (similar to that 

 of the Spongeliidae)" Genera Psammina, H. ; Holopsamma, Crtr. ; 

 Psammopemma, Marshall. FAMILY STANNOMIDAE, H. " Keratosa with 

 a fibrillar spongin skeleton, composed of thin, simple, or branched spongin 

 fibrillae, never anastomosing or reticulated. Pseudo-skeleton composed 

 of xenophya . .' . which are crowded in the transparent maltha, never 

 in the homogeneous fibrillae. Canal system vesicular ... on the 

 Leuconal type. . . \ ." Genera Stannophyllum, H. ; Stannarium, H. ; 

 Stannoma, H. 



GRADE IV. MYXOSPONGIDA, Soil. 

 Sponges devoid of a skeleton in any form. 



FAMILY 1. OSCARELLIDAE, Ldf. With spherical ciliated chambers. 

 G enus Oscarella, Vosm. (Fig. 41). FAMILY 2. HALISARCIDAE, O'.S. With 

 elongated, sack-like ciliated chambers. Genera Halisarca, Duj. : Bajulus, 

 Ldf. ; Hexadella, Tops. 



APPENDIX TO CLASSIFICATION. 



Under the namea Octactinellida and Heteractinellida, Hinde (1887) 

 has described two groups of Palaeozoic sponges, each with a very aberrant 

 type of spicule, which cannot be brought either under the triaxon or 

 tetraxon type. 



In the Octactinellida, represented by the single genus Astraeospongia 



