120 Mr. H. J. Carter on Fossil Sjponge-spicules of 



less shortened in proportion to its thickness and the inflation 

 of its rounded extremity. 



Such spicules are represented in figs, 76 and 77 respec- 

 tively ; and as they greatly exceed in number all other large 

 sorts in the existing Pachytragiaj (being tlie spicule of the 

 mass), so they abound in a fossil state in this deposit, both 

 entire and fragmentary, of various sizes, from l-5th of an inch 

 downwards, with proportional thickness. 



As in no instances are such large stout spicules of this kind 

 to be found in any species but tlie Pachytragire, so, for the 

 most part, the whole of the fossil ones must be infeiTcd to 

 have come from sponges of this group. With one exception, 

 however, viz. Dercitus niger (Ann. vol. vii. Jan. 1871), which 

 differs from all others of the Pachytragise Avith which I am 

 acquainted in having no acerate spicule, while its body, being 

 crammed full of stout teniate ones in which the shaft but 

 slightly exceeds in length the arms, finds its representative in 

 fig. 71, which, with shorter shaft and of various sizes below 

 this figure, is nearly as abundant as any other form of spicule 

 in the Haldon deposit. 



Lastly, we come to the smaller spicules ; and here there are 

 only fom* figures, 40, 41, and 42, 43, and 55, and 56 which 

 can with any certainty be assigned to species like the existing 

 sponges. 



The first two evidently belong to the Dactylocalycidje ; but 

 their smalhiess and differences respectively from those figured 

 in PI. VII., being strongly marked, may be easily appreciated 

 by comparison. 



In fig. 43 we immediately recognize a sharp- pointed bi- 

 hamate spicule of large size, which may represent the Espe- 

 riadfB, its usual companions (viz. the anchorates) being as- 

 sumed to have been too small to have survived the tiitiiration 

 of the deposit, or the solvent effect of the pctrifactive process. 



Figs. 55 and 56 are lateral and upper views respectively 

 of the globular crystalloids, or siliceous balls, which cha- 

 racterize the crust of the Geodidaj, and which so abound, of 

 many sizes below the figure, and of so many shapes between 

 spheroidal and oval, that their presence in regard to numbers, 

 not less tlian their variety in size and form, distinctly points 

 out their origin from the disintegration of more than one kind 

 of Geodia. 



Of the rest, figs. 44, 45, 46, and 47 are figures of two spi- 

 cules which are equally beautiful and abundant, but to whose 

 origin nothing that I know of among existing sponges gives 

 me any clue. They may have belonged to the Dactylocaly- 

 cidje, and future observation may throw some light upon their 



