UPPER, OR FLINTY CHALK. 165 



The depth of the cup-hke cavity is in the proportion of one-third of 

 its longest diameter, the latter being nearly equal to the length of the 

 entire fossil, which varies from three to eight inches. The margin, or 

 border of the cup, is about 0*3 inch in thickness, and exposes the edge of 

 the enclosed zoophyte. The base is perforated by several foramina, 

 through which the processes of attachment have passed ; and it is not un- 

 usual for the openings to be partially filled with the remains of these ap- 

 pendages. These are the only external indications of the original in the 

 perfect siliceous specimens, the substance of the zoophyte being com- 

 pletely enveloped in flint, except at the margin and base; but upon 

 fracture, sections are obtained that distinctly display its form and structure. 

 When preserved in chalk, the porous or spongeous texture is very ap- 

 parent, and these examples are more or less deeply coloured with an 

 ochraceous or ferruginous stain*. 



That the original was a zoophyte of a cyathiform shape is very clearly 

 established; and in all probability, it bore considerable resemblance to S. 

 infundibuliformis, or S. crateriformisf. 



Localities. Upper chalk, near Lewes. 



1 5. Spongus labyrinthicus. Tab. xv. fig. 7. 



Body hemispherical, turbinated, or subcylindrical ; the superior surface 

 marked with flexuous depressions ; base perforated. 



The figure sufficiently explains the usual form of these fossils. The 

 base has an irregular foramen for the passage of the processes of attach- 

 ment. The upper surface is almost flat, and is marked with flexuous anas- 



* Mr. Townsend remarks, " that many of these fossils are compressed, and others havp 

 their margin folded back without being fractured ; on the otlier hand, there are numbers which 

 have evidently been fractured and have sharp edges. The former are probably sponges of the 

 infundibuliform species ; the latter, I am persuaded, are cup-corals. Such were the corals of 

 M. Guettard, as appears by the Memoirs of the Academy of Paris for the year 1751." 



f There are several recent sponges that possess a cyathiform figure, viz. Spongia infundi- 

 bulifm-mis, Wernerian Transactions, Vol. 1, p. 562. S. crateriformis, Pallas, Zooph. p. 386. .S'. 

 scypha, Wernerian Trans. Vol. 2, p. 107. The shape of the last mentioned is that of an inverted 

 cone, with a very short stalk, which is of a corky nature internally, but porous superficially, 

 like the other parts ; the hollow spreads like the bowl of a wine glass, becoming smaller at the 

 bottom. 



