FROM THE YORKSHIRE CHALK. 



15 



4. Sp. ampulla. — Bladder-shaped, covered with irregular depressions ; 

 stem equal to the hody in length ; fibres of the root short and thick ; 

 central cavity cylindrical, half the depth of the body. Fig. 10. 



^nr^^msi^ This species is not so rare as the pre- 



ceding, but is seldom met with in such 

 complete preservation as the specimen 

 figured, {fig. 10.); the greater number 

 of those which have been found, are 

 compressed and distorted. Two or 

 three weathered specimens in my pos- 

 session show very clearly that the cen- 

 tral cavity is in the shape of a short, 

 thick cylinder, suddenly terminating 

 about the middle of the body: the 

 length of the specimen is about nine 

 inches and a half. 



5. Sp. spinosa. — Globular, unattached, covered partly with oval notched 

 plates, overlying each other, partly rough, covered with irregular de- 

 pressions : armed with from eighteen to twenty spines : internal struc- 

 ture fibrous, radiating from a point in the circumference. Spines 

 varying much in size, hollow, covered with an appearance of pointed 

 scales overlying one another. Fig. 1 1 . 



This most singular fossil has I believe, only been found in 

 two localities ; one of which is the cliff about a hundred 

 yards west of the Danes' Dyke, and the other a quarry north 

 of Marton, probably where the same bed appears on the sur- 

 face. It is rare ; I only know of five specimens, of which 

 one was found by my friend Mr. W. H. Dykes, and is now 

 in the Museum of the Hull Literary and Philosophical So- 

 ciety. I have indeed heard of a fossil in the collection of 

 Mr. Bowerbank, which from the account given to me by 

 Mr. Charles worth, may probably be the same species, but 

 I have never been fortunate enough to obtain a sight of it. 



The general appearance, when most perfect, is that of a 

 small Cidaris, with the spines attached : when imperfect, it 

 would probably be taken for one of the small globular sponges, 



