AFFIXITIES OF THE GEXES PE0T0SP0:NGIA. 363 



after a study of the -whole of the material which has come under my 

 observation, I feel no difficulty in definitely assigning to Protosponrjia 

 its place amongst the other sponges. Moreover, as Dr. Hicks's figure 

 of his specimen is almost purely diagrammatic, I have ventured to 

 insert here a fresh drawing of part of it, kindly made for me by my 

 friend Mr. T. H. Thomas, of Cardiff. The great interest which must 

 necessaril}' attach to the best-preserved specimen of the oldest known 

 sponge renders excuse for this second representation of it needless. 



3. Desceiptiox. 



The specimens on which Salter's description was based were 

 crushed and flattened forms in which the skeleton appears as raised 

 lines or narrow thread-like ridges arranged in a lattice- like reticula- 

 tion on the bedding-planes of the slate which serves as a matrix. 

 Dr. Hicks's specimen (fig. 1), on the other hand, presents us with the 



Fig. 1. — Part of tlie specimen 0/ Protospongia feuestrata, in the 

 IVoodwardian Mtrscmii. (]S'atural size.) 



spicules of the sponge in their original form, unaltered, or but slightly 

 altered by pressure, and standing out in free relief from the weathered 

 matrix, which has in several places been artistically cleared away 

 from beneath them. 



In this state of perfect preservation the spicules are clearly not 

 fused together into a continuous network ; they are separated and 

 free, and only form a network by the interlacing of their extremities. 

 Their form also is somewhat different from that of the s^ncules of 

 crushed specimens. 



Form of tJie Sjncules. — Each sj^icule is quadriradiate, with its 

 centre raised some slight but variable distance above the plane in 

 which its rays terminate. Its general form may be most easily 

 described by imagining it as modelled upon a low four- sided pyra- 

 mid, the centre of the spicule lying upon the apex, and its four rays 



