Classification of the Spongida. 181 



zontally, clathrously, and dendritically in the substance of 

 shells, especially those of the oyster, here and there provided 

 with papillary heads which project through the surface of the 

 shell ; or fixed and unconnected with shells, massive, hemi- 

 spherical, nodular ; or crest-like, compressed, with parallel 

 sides, thick and semicircular ; or vase-like, poculous, stipitate, 

 ribbed nodosely (Neptune's cup). 



Group 11. Compacta. 



Sarcode colourless, pale yellow, ochraceous. Skeleton 

 compact, and so minutely cancellated as to form with its 

 sarcodal contents a homogeneous soft, dense, fine, felt-like 

 structure, interrupted only by the branching canal-systems, 

 which are correspondingly reduced in calibre, and thus rendered 

 more or less indistinct. Surface smooth, compact, often villous 

 or asbestiform, from the projection of the ends of the dermal 

 spicules. Vents not prominently marked. Pores in the inter- 

 stices of the dermal reticulation. Texture compact, cork- 

 like. Spicules of two kinds, viz. skeleton- and flesh-spicules. 

 Skeleton-spicule of one form only, viz. pin-like ; shaft 

 smooth, curved, fusiform, more or less taperingly pointed ; 

 head elliptical and subterminal ; with every variety between 

 this and the simple acuate, in which there is no inflation at all. 

 Flesh-spicule minute, smooth, curved, cylindrical, centrally 

 or subcentrally inflated. Or the skeleton-spicule may be 

 smooth, acerate, fusiform, more or less sinuous, especially 

 towards the centre, from which in the larger kinds a third 

 sinuous arm may be developed at right angles to the other 

 two. Forms massive, sessile, compressed pedicelled, bacillary 

 or fig-shaped ; or free and waterworn, more or less rounded, 

 when growing over and absorbing deciduous univalve shells ; 

 or branching coalescently, branches solid, terminating in 

 rounded extremities singly, or united laterally so as to present 

 short digitated (toe-like) extremities ; separated or united into 

 a general mass which is sessile ; sometimes parasitic on Fuci. 



Group 12. Laxa. 



Sarcode colourless, pale tawny, red, bright carmine, and 

 purple. Structure crumb-of-bread-like, more or less open and 

 cancellated. Surface uniformly granular or corrugated, villous, 

 or smooth and pustular. Vents scattered over the surface 

 generally, or distinct, on mammiform projections ; excretory 

 canal-systems largely developed, sometimes cavernous. Pores 

 dispersed throughout the interstices of the dermal reticulation 

 generally, or congregated into pustular heads. Texture light, 



