1886.] POSITION AND CLASSIFICATION OF SPONGKS. 581 



I. Group LiTHisTiDA, Zittel. 



Body stony, with a central gastral cavity or numerous vertical 

 tubes. Spicules more or less clearly tetraxon, often branched. 

 Besides these, sometimes monaxon spicules and flesh-spicules. The 

 skeleton-spicules are interwoven so as to form a dense skeleton. 



1. Familia Rhizomorinid^, Zittel. 



Spicules irregularly branched ; form irregular fibres, or are loosely 

 interwoven. Forked anchors always present. 



Arabescula, Carter ; Corallistes, Schmidt ; Heterophymia, Pomel ; 

 Seliscotkoti, Zittel ; 3facAndrewia, Gray ; Azorica, Carter ; Leioder- 

 matium, Schmidt ; and the fossil genera : — Cnemidiastrum, Coral- 

 lidium, Hyalotragos, Pyrgochmda, Discostroma, Leiodorella, Episto- 

 mella, Platychonia, Bolidium, Astrobolia, and Chonella of Zittel; 

 Plococonia, Pomel ; Chenendopora, Lamouroux ; Verruculina, Zittel; 

 Amphithelion, Zittel ; Stychophyma, Pomel ; Allomera, Pomel ; 

 Pleuromera, Pomel ; Perimera, Pomel ; Meta, Pomel ; Marisca, 

 Pomel ; Pomelia, Zittel ; Jereica, Zittel ; Coelocorypha, Zittel ; Scy- 

 talia, Zittel; 8tackyspongia, Zittel; Pachinion, Zittel. 



2. Familia Anomocladinidje, Zittel. 



Spicules rod-shaped with terminal tufts of l)ranches. The approxi- 

 mating ends of the spicules coalesce and form knots. In this way a 

 regular triaxial network is formed. 



Vetulina, Schmidt; and the fossil genera Mastosia, Cylindrophyma, 

 Melonella, and Protachilleum, Zittel, and Palceomanon and Astylo- 

 spongia, Roemer. 



3. Familia Tetracladinid.e, Zittel. 



Spicules tetractinellid with terminal branches. 



Theonella, Gray ; Rhacodiscula, Zittel ; Discode7-mia, Bocage ; Ka- 

 /jV/ps2«, Bowerbauk ; Collectella,^chm\At; Collinel la, Schmidt; and 

 the fossil genera : — Aulocopium, Oswald ; Phyinaiella, Aulaxinia, 

 Callopegma, and Trachysycon, Zittel ; Siphoniu, Parkinson ; Halli- 

 rhoa, Jerea, Lamouroux; Margiiiospongia, d'Oibigny ; Nelumbia, 

 Pomel ; Polyjerea, Fromentel ; Asfrocladiu, Zitti'l ; Bulospongia, 

 Hinde ; Thecosiphonia, Zittel; Calymmatina, Zittel; Turonia, Mi- 

 chelin ; Kalpinella, Thamnospongia, and Pholidodadia, Hinde ; Ra- 

 gadmia, Zittel ; Plinthosella, Zittel ; Spongudiscus, Zittel ; Phyma- 

 plectia, Hinde ; Rhopalospongia, Hinde. 



To this Subordo also the fossil family Megaraorinidae belongs. 



II. Group C HO RisTiDA, Sollas. 

 With tetraxon spicules of regular shape. 



i. Tribus Tetradina, Sollas. 

 The chief spicules are tetract, with equal rays and candelabras. 



i. Subtribus Micro camei-ce, nov. 

 With small chambers. 



