1886.] POSITION AND CLASSIFICATION OF SPONGES. 591 



'With lithistid irregular tetraxon spicules 18. 



With tetraxon spicules of irregular shape; 

 askeletous forms with large chambers, which 



. „ J have large outlets (19-) 



I With monaxou tylostylote spicules (20.) 



Without supporting spicules ; flesh-spicules 

 when present polyact, with small chambers 

 (^ which have narrow outlets (21.) 



(Spicules quite irregular 18. Rhisomorinidm. 

 Spicules rod-shaped, with terminal tufts of 

 branches 19- Anomocladinida. 

 Spicules tetractin, with terminal branches 20. Tetracladmidce. 



/The spicules are chiefly tetracts with equal rays 



I and candelabras 22. 



(19.)-^ There are large tetract spicules with three 



equal rays lying tangeutially in or beyond the 

 l^ surface, and one differentiated, radial ray ... (23.) 



f With small inconspicuous ciUated chambers 



with small outlets 24. 



22. 



1 v» 



wide outlets (25-) 



„. f With candelabra 21. Corikidce. 



24. 



] With large conspicuous ciliated chambers with 



\ With simple tetracts 22. Pachastrellida. 



(25.) I ^j 



With scattered tetracts, triacts, diacts 23. Plakinidm. 



Without spicules 24. Oscarellidm. 



(Tetracts with diiferentiated large centripetal 

 ray and large tangential rays numerous 26. 



Tetracts with differentiated large centripetal 

 ray rare, with small tangential rays (27.) 



(,„ f With spherasters , 25. Geodidcs. 



\ Without spherasters 28. 



r Flesh-spicules euaster and oxyaster 26. Stellettidce. 



28. -! Flesh-spicules spirastrella 27. Thcneidm. 



[ Flesh-spicules spirula and sigmata 28. TetillidcB. 



(27.) Without flesh-spicules 29. Tethyopsillidce. 



(20.)- 



' The widened distal ends of the radial spicule- 



bundles divide the regular subdermal cavities 



into ectochonse or vestibules at the entrance 



of the inhalant canals 30. Tethydm. 



. Between the distal ends of the radial spicule- 



bundles ecto- and entochonse are found 31. Bollasdlidm. 



I The inhalant pores lead direct into the inhalant 



\^ canals 29. 



r With spirastrellid flesh-spicules 32. Spirastrellidce. 



29. -I With sigmate flesh-spicules 33. StAeramatide, 



\ Without flesh-spicules 34. Suberitidcs. 



(31.) { 



With polyact flesh-spicules 35. ChondrilUd<B. 



Without flesh-spicules 36. Chondrosidce. 



