8 io THE ANIMAL KINGDOM. 



nected to central cavity by a complicated exhalent canal-system, VosmaeraLeucettt, 

 in part, or placed radially to the wide exhalent canals, the layer of ampullae being 

 thrown into {Q\fe,Polejna=Leurilla; (m) Leuconidae \ a ramified inhalent and exhalent 

 canal-system, and spherical ampullae, Leucetta in part, Leuconia (=Leucetta, Leu- 

 caltis, Leucandra in part), Pericharax (= Leucandra in part) ; (iv) Teichonidae, 

 external surface differentiated into two planes, one pore-bearing, the other with 

 oscula, Teichonella, Eilhardia ; the internal organisation of the latter does not differ 

 from that of Leuconidae (Pole'jaeff) *. 



Extinct group, Pharetrones of Zittel, probably a sub-group of Leuconidae. 



II. PoriferaNon-Calcarea=Fibrospongiae\ skeleton rarely absent, composed of 

 either siliceous spicules or spongin fibres; the spicules are either isolated, or 

 united by silica or spongin ; gastric system belonging to either type (3) or (4) ; 

 see p. .794. 



1. HyalospongiaeHexactinellidae\ skeleton wholly siliceous, spicules triaxile, 

 either isolated or united by silica into a trellis-work ; canal-system known only in 

 Euplectella, belonging to type (3), see p. 794 ; marine, and for the most part deep- 

 sea forms ; extend from the Silurian to the present epoch ; two sub-orders, (i) Dicty- 

 onina : spicules united by the tips of their arms ; skeleton a trellis-work with square 

 or irregular meshes ; flesh-spicules present or absent, e. g. Farrea, Aphrocalistes^ 

 Dactylocalyx, and a large number of fossil forms, including the Ventriculitidae ; (ii) 

 Lyssakina : spicules united only by protoplasm, or a small quantity of silica ; flesh- 

 spicules usually numerous and of very various forms, e. g. Hyalonema, Euplectella^ 

 Holtenia, Pheronema, and fossil forms including the Receptaculitidae. 



2. Spiculispongiae : skeleton very rarely absent ; spicules generally indepen- 

 dent, united either by interlocking processes or into bundles by organic material, 

 with five sub-orders : (i) Lithistina : body strong and massive, a central cloaca, or 

 scattered oscula ; cloaca frequently replaced by vertical tubes ; spicules tetraxile or 

 branched regularly, often covered entirely or at their extremities with knobs, or 

 much divided, for the most part firmly interlocked; monaxile needles frequent; 

 flesh-spicules often present ; extend from the Silurian to the present epoch, the 

 majority extinct ; (ii) Tetractina : spicules to a great extent tetraxile ; large monaxiles 

 common ; both forms frequently disposed radially ; stellates and globules almost 

 always present ; Geodidae, e. g. Geodia, Pachymatisma, &c. ; Ancorinidae, e. g. Stel- 

 letta, Tetilla, Craniella ; Plakinidae ; Corticidae ; (iii) Oligosilicina : skeleton, if pre- 

 sent, composed of isolated stellates, canal-system belonging to type (3) or (4) ; 

 Chondrosidae ; Halisarcidae (=Myxospongiae), no skeleton, Halisarea, Oscarella; 

 (iv) Pseudotetraxonia : body with a radial structure, a cortex usually well-defined, 

 spicules for the most part monaxiles ; stellates may also be present, canal-system 

 belonging to type (4) ; Tethyadae, e. g. Tethya ; (v) Clavulina, firm in consistence ; 

 a cortex common ; a radial character sometimes visible in skeleton ; spicules fre- 

 quently knobbed ; canal-system belonging to type (4), occasionally to (3) ; Polymas- 

 tidae, e. g. Polymastia, Rinalda ; Suberitidae, e. g. Poterion, Suberites ; ? Clionidae. 



3. Cornacuspongiae : skeleton consists either of principally monaxile spicules, 

 which are united by more or less spongin, or of spongin fibres with or without 



1 For classification and genera, see the works of Polejaeff and von Lendenfeld cited in the 

 literature ; for a table showing the correspondence of Polejaeff s genera with Haeckel's genera and 

 species, Vosmaer's Porifera, p. 389. 



