256 G. J. HINDE. — SIL1CEOUS ROCK FROM THE 3i 



referred to the genus Reniera, they are very common in fossil sponge 

 beds, ranging from the carboniferous rocks upwards. 



Acuate or styliform spicules 'Stift, Vos.) (figs. 1 1-17] are also nume- 

 rous. boîh smooth and microspined rorms are présent ; with them 

 are the nearly alHed spinulate forms (Stecknadel, V.) (figs. 21-26 

 with prominent roanded heads. 



Thèse various forms of Monactinellid spicules are the skeleton or 

 body spicules of several différent gênera of this group of sponges. 

 Though it is now impracticable to refer them to particular gênera, it 

 may be safely assumed that they represent at least from 20 to 2 3 différent 

 species. Besides thèse skeletal spicules a few of the more minute flesh- 

 spicules have been preserved; thus there are some small « anchorates 0 

 (Anker, Vos. not more than o m ,o6 in length (figs. 27, 28, 29) which 

 closelv correspond to thoseinexisting sponges ; also C-shaped spicules 

 (Haken.y .) (fig. 3o like those of Esperella ; clasp-hookforms (Pflug- 

 scharspangen, V.) 'fig. 3i) belonging to the exisîing genus Hamacan- 

 thus; and chessmen spicules or sceptrellas fig. 32j resembling those of 

 the existing gênera Sceptrella or Latrunculia. Further a minute 

 elongated spined form (fig. 81) may be the flesh spicule of a species of 

 Spirasirella. 



2. Tetractinellidae. 



The most numerous of the detached spicules of this division of 

 sponges are the four rayed forms or Galthrops (Vierstrahler, V 03 . 

 (figs. 45 -5 i, 53)probably belonging to the genus Pachastrella. They 

 vary considerably in size, as may be seen by the figures; the rays are 

 usually smooth, through microspined forms occur. 



There are several différent forms of the trtfrdof zoie-spi :ules of 

 Geodites and aliied gênera (figs. 56-70 in which there is an unusually 

 long, slightly curved and gentlv tapering shaft igenerally now broken 

 and incomplète and three head-rays at its summit, which either pro- 

 ject forwards or are recurved. In some spicules the head-rays bifurcate 

 and are widely extended horizontally (figs. 54, 55), whilst the shaft is 

 nearly obsolète. 



The ovate or reniform spicules 'figs. 71-76), similar to those of the 

 dermal crust of the récent Geodia, are very abundant and with them 

 are mingled stellate and globostellate spicules like those of the 

 existing genus Tethya (figs. 77-80 . 



