116 Mr. H. J. Carter on Fossil Sponge-spicuUs of 



whose form is too common to be of any value specifically, are 

 far too delicate to siu'vive the amount of tritui'ation tln-ough 

 which the coarser forms of the spicules of the other Pachy- 

 tragiaj might pass, as we see in this deposit, for the most part, 

 unaltered. 



Nor have we met with any stellates (spicules) , especially the 

 larger ones of Tethya lyncurium and its like, better named 

 by Dr. Gray ^^ Donatia^'' to separate it from the tnie Tethyadas, 

 of which T. cranium is the type, although the little globular 

 crystalloids (spicules), or little " siliceous balls," as they have 

 been termed, which characterize the crust &c. of the Geodidee, 

 are extremely abundant. 



If, then, there are none of these stellates present, which, in 

 some species of Donatia, are equal in size to the larger glo- 

 bular crystalloids of the Geodidge, we can hardly wonder at 

 the entire absence of the minuter stellates of the Pac]iytragia3 

 generally, or of any other spicules so minute that a quarter-inch 

 compound power is required to make them visible. 



Whether Donatia [Tethja lyncurium) and its like existed at 

 this period may be another question which the limited exami- 

 nation of the Haldon sand made by Messrs. Vicary, Parfitt, 

 and myself is in no way sufficient to answer ; for it may be 

 assumed that, in a stratum 25 feet thick which is almost 

 entirely composed of grains of sand and the spicular remains 

 of various sponges, almost any amount of examination, most 

 especially ours, must indeed be " limited." 



Again, it is evident that there were sponges like the Es- 

 periada3 (Gray) present, if bihamate spicules be allowed to de- 

 termine this ; for here, also, the other spicular element of these 

 sponges, viz. the anchorates, are so much smaller, for the most 

 part, than the bihamates in the existing species, that the an- 

 chorates, like the stellates of the Pachytragiaj, may have dis- 

 appeared, either by the triturative effect of the sand at the 

 time of deposit, or by the solvent effect of the fluids which 

 have since percolated through it. 



Lastly, it is possible that, in solid masses of flint, such mi- 

 nute spicules may be found to be most perfectly preserved, 

 and in some parts representatives of the deep-sea sponges may 

 be found entire ; but neither appear, elementarily or entire, in 

 the sandy grit of Haldon Hill or Black Down, so far as our 

 observation has extended, nor, for the reasons above stated, 

 is it likely that one ever so extended would be more suc- 

 cessful. 



Still there are a great number of forms in the Haldon sand 

 which have living representatives, and probably a great many 

 which have none. Let us, then, first sec generally how far we 



