Sponges from the Atlantic Ocean. 479 



Fig. 42. Isodidya spinispiculum, spicule of. Scale l-24tli to l-6000tli 



inch. 

 Fiff. 43. Microciona intexta : a, skeleton-spicule ; h, bihamate ; c, bihamates 



in the mass. Scale l-24th to l-6000th inch. 

 Fig. 44. Xanthidium bicirratmn. Scale l-12th to 1-GOOOth inch. 



Plate XVI. 



Fig. 45. Geodia nodastrella. a, " zone-spicule," viewed laterally ; h, end 

 view of head; c, ''body "or large skeleton acerate spicule ;^^, 

 " anchoring-spicule " fluked and forked ; e, body-stellate ; /, sili- 

 ceous balls of crust, globular and elliptical forms ; //, nodostellate 

 of dermis and crust ; h, dermal acerate : all on the same scale, 

 viz. l-48th to l-1800th inch, i, body-stellate, more magnified ; 

 h, nodostellate of dermis and crust, more magnified. 



Fig. 46. Geodia megastrella on a fragment of Corattistes : a, sponge ; 

 b, aperture or common vent ; c, pore-areae ; d, fragment of 

 Corallistes Boxverhankii. 



Fig. 4:6'. The same, spicules of. o, zone-spicule ; &, less frequent form of 

 headof zone-spicide; c, " body" or large skeleton acerate spicule ; 

 d, anchoring-spicules, fluked and forked ; e, megastrella, arms 

 microspined ; /, body-stellate ; g, siliceous balls of crust, globular 

 and elliptical forms ; h, dermal stellate ; i, dermal acerate : all 

 on the same scale, viz. l-48th to l-1800th inch, k, megastrella, 

 more magnified ; /, body-stellate, more magnified ; in, dermal 

 stellate, more magnified. 



Fig. 47. Geodia megastrella, var. Icsvispina. a, zone-spicule ; b, body or 

 large skeleton acerate spicule ; c, anchoring-spicules, fluked and 

 forked respectively ; d, megastrella ; e, siliceous balls of crust ; 

 /, stellate of dermis and crust ; g, dermal acerate : all on the 

 'same scale, viz. l-48th to l-1800th inch, h, megastrella, more 

 magnified; i, spines broken ofl"; k, dermal stellate, more mag- 

 nified. 



Fig. 48. Tethya cranium, var. infrequens. a, projecting forked anchoring- 

 spicule, with arms truncated and terminating in little cup-shaped 

 excavations with serrated margins respectively ; c, projecting 

 fluked or anchor-like anchoring-spicule : scale l-48th to 1-GOOOth 

 inch, h, extremity of arm of forked form («), more magnified. 



Fig. 49. Tethya cranium, var. abyssonim : a, two bihamates, magnified to 

 show that they are spinous. Scale l-6th to 1-GOOOth inch. 



Fig. 50. Puchastrella parasitica, a, radiate skeleton-spicule, showing that 

 its arms are thrice forked ; b, shaft, prolonged above as well as 

 below ; c, acerate skeleton-spicule ; d, spinous bacillary flesh- 

 spicule ; /, minute stellate : all on the same scale, viz. l-24th 

 to l-6000th inch, e, spinous bacillary flesh-spicule, more mag- 

 nified. 



Fig. 51. Microciotta mimittda : a, large skeleton-spicule; i, different forms 

 of its head ; c, slender acuate ; d, bihamates. Scale l-24th to 

 l-6000th inch. 



Fig. 52. Corticium iMrasiticum, spicules of. Scale l-24th to l-6000th 

 inch. 



Fig. 53. Cometella simplex, natural size. 



