148 SPONGES 



FAMILY 4. STELLETTIDAE, Soil. Megascleres, triaenes, and rliabdi ; 

 canal system aphodal ; ground substance of choanosome sarcenchymatous. 

 SUB-FAMILY (a). HOMASTERINA, Soil. Never more than one form of aster. 

 Genera Myriastra, Soil. ; Pilochrota, Soil. SUB-FAMILY (6). fEuASTE- 

 RINA, Soil. With two kinds of euasters. Genera Anthastra, Soil. ; 

 *Geodites, Crtr. [Cret. Eoc.]; jStelletta, O.S. [Cret. Eoc.]; Dragmastra, Soil. 

 SUB-FAMILY (c). SANIDASTERINA, Soil. With euasters and sanidasters or 

 amphiasters. Genera : Ancorina, O.S. ; Tribrachion, Welt. (Fig. 25); 

 f Tethyopsis, Stew. [Cret] ; Disyringa, Soil (Fig. 26) ; Stryphnus, Soil ; 

 Seiriola, Han.; Sanidastrella, Tops. SUB -FAMILY (d). RHABDASTERINA, 

 Soil. With euasters and microrhabdi. Genera Ecionema, Bwk. ; 

 Papyrula, O.S. ; Psammastra, Soil. ; Penares, Gray ; Algol, Soil. 



Demus y Sterrastrosa, Soil. The characteristic microsclere a sterr- 

 aster. 



FAMILY 5. JGEODIDAE, Gray. With triaenes. SUB-FAMILY (a). 

 IERYLINA, Soil. Megascleres, orthotriaenes, and rhabdi, never ana- 

 triaenes or protriaenes ; somal microsclere a microrhabdus or spherule. 

 Genera ifErylus, Gray [Eoc.] ; Caminus, O.S. ; Pachymatisma, Bwk. 

 SUB-FAMILY (6). JGEODINA, Soil. Megascleres rhabdi, orthotriaenes, or 

 dichotriaenes, frequently also protriaenes and anatriaenes. Somal micro- 

 sclere, an aster with numerous rays. Genera Cydonium, Flem. ; jGeodia, 

 Lam. [Cret] ; Synops, Vosm. ; Isops, Soil. FAMILY 6. IPLACOSPONGIDAE, 

 Gray. Megascleres pin-shapecl monaxons (" tylostyles "), no triaefles. 

 Genera Placospongia, Gray ; Antares, SolL ; Physcaphora, Han. ; *Ehax- 

 ella, Hinde [Jur.]. 



Genus incerti sedis * Ophirhaphidites, Crtr. [Cret.]. 



SUB-ORDER 2. LITHISTIDA, O.S. 



Tetractinellida with a rigid skeleton, due to interlocking of special 

 (secondary) spicules, desmas. 



The classification which follows is that of Sollas, founded upon a study 

 of the living forms. In addition there are numerous fossil forms, not 

 sufficiently well characterised to be assigned a definite place in this 

 system, such as the family Rhizomorina of Zittel, which should be divided 

 amongst the two families Corallistidae and Azoricidae ; these will be found 

 appended at the end of the system. The new groups and families created 

 by Rauff, whose studies are not yet completed, are indicated in square 

 brackets in their proper places. 



TRIBE 1. HOPLOPHORA, Soil. 



With special ectosomal spicules and usually some form of microscleres. 



Demus a ^Triaenosa, Soil. The ectosome contains megascleres, 

 typically triaenes, sometimes, however, monaxons (styles Desmanthidae ; 

 rhabdi Sulcastrella) ; canal system aphodal. 



FAMILY 1. |TETRACLADIDAE, Z. With tetracrepid desmas and micro- 

 scleres. Genera f Theonella, Gray [Eoc.]; f Discodermia, Boc. [Eoc.]; 

 Racodiscula, Z. ; Kaliapsis, Bwk. ; Neosiphonia, Soil. ; Rimella, O.S. ; 

 Gollinella, O.S. (Fig. 28, B) ; Sulcastrella, O.S. ; *Phymatella, Z. [Cret] ; 

 *Aulaxinia. Z. [Cret] ; *Callopegma, Z. [Cret] ; * Trachysycon, Z. [Cret] ; 



