Intkoductokv. 27 



The rods of the vertical and horizontal bundles are for the most part 

 smooth throughout their entire length; they afford no evidence of being 

 stauractine, but, as suggested in tlie diagnosis of the family given by Rauff, 

 are apparently extremely elongated diactins. The outer wall of these sponges 

 usually carries a regularly (juadrate mesh produced by large pentactins 

 standing at each angle of the quadrules. These outer quadrules usually, 

 though not necessarily, correspond with the varying quadrules of the inner 

 reticulum, and it is not at all certain that the outer meshes are greatly sul)- 

 divided. This outer or dermal layer may also carry projecting spicules oi 

 various forms, spinules, umbrella-shaped clavules and echinated stauractins, 

 which will be more fully described in tlie following pages. The surface may 

 also bear projecting ornamental lamellae and ridges like those in Euplectella, 

 and strongly developed tufts of stout rods, as in Physospongia and Hydnocebas. 

 To the thin space intervening between the outer and inner surfaces of the 

 skeleton are ascribed some normal hexactinellid and minor modified forms 

 of spicules. 



The variations in form independent of essential alteration in structure are 

 most noteworthy. Some of the Dictyosponges are obtusely or acutely obconical 

 with a simple exterior ; other obconical forms have a highly nodose and tufted 

 surface with, sometimes, clusters of pendulous pouches; many are distinctly 

 prismatic, some bear strong concentric annulations and vertical ridges, a few 

 have the form of large saucers, others of graceful vases Avith slender neck and 

 expanded bowl, and in two genera the form is almost cylindrical and has a 

 broad fringe or frill about its flattened base. 



One should pause to reflect that these ancient organisms with their 

 manifold variety of graceful and striking shapes, were not the sombre bodies 

 we find them to be in the rocks, but in life formed the most delicately 

 woven fabrics of glass, latticed vases, urns and cups of the rarest delicacy 

 and beauty. They must have been, Avhen denuded of their sarcode, among 

 most exquisite structures of the past, as their descendants are of tlie 

 the present. Nothing for example, could have surpassed the graceful 

 filigreed chalice of Botryodictya rarnom, with its slender, tufted pedicel 

 expanding above into a cup ornamented with pendant pouches. 



Forms like those just mentioned as having a flattened transverse extremity, 

 raise an important question as to the existence in these sponges of a terminal 

 sieve-plate like that in Euplectella. The determination of this point is 

 essential not only to a proper conception of the limitations of the family 



