15 



form figures bearing somewhat of a stellated appearance. A slight 

 sketch, showing the form of the surface of this fossil, as given by Walch, 

 is shown Plate I. Fig. 14. 



Plate I. Fig. 12, is an echinite found in the green silicious sand, so 

 frequent in several parts of Wiltshire. The figure here given is mag- 

 nified to about twice the size of the fossil. Round the superior opening 

 of this echinite may be seen a remarkable extension of the appendage 

 above mentioned; formed chiefly in roundish plates, connected toge- 

 ther by numerous short filaments, and reaching over nearly a third part 

 of the surface. In another specimen, these plates are hexagonal, and 

 exactly fitted to each other. Plate I. Fig. 13, is another echinite from 

 the same part, which is particularly interesting, from its appearing to 

 be highly illustrative of the fossils above mentioned. The anal append- 

 age is here seen, with a trelissed surface, almost exactly similar to that 

 of M. Walch's fossil, and extending so low down, as to cover nearly 

 one half of the echinite. If, indeed, this surface had extended over 

 the whole echinite, it would have very closely resembled M. Walch's 

 fossil, and have yielded us no further information: but sufficient of the 

 inferior part of the surface of the echinite is left uncovered, to allow us 

 to discover, that it has all the characters of a beautiful variation of the 

 C. diadema. 



Still, however, we are without any positive information as to the 

 nature and office of this part, which is so singularly organised. It is on 

 future specimens, and on further observations on the living animal, , 

 that we must depend for information on this subject. Whether this is a , 

 permanent appendage or not; whether it belongs to particular species 

 only ; or whether it is a part essential to the animal of each species, . 

 serving to model the increasing shell, or to perform some other im,- 

 portant service ; are questions which must be answered by some future 



investigator. 



The genus C. assulata* of Klein, is undoubtedly unfounded^ since the 

 distinction, which is derived from a distinct view of the assuiae, or plates, , 



