TURBAN ECHINITES, 313 
of the plates vary in size from mere granules, or papille, to 
large mamillated tubercles ; they serve for the attachment 
of movable spines, which also present great variety of form 
and ornament. The spines have a cup-like cavity at the 
base which fits on the papillee, and in many species are only 
supported by the capsular envelopment of the common inte- 
gument ; but in others, the large spines are attached by a 
ligament which passes from the centre of the socket, and is 
received in a perforation of the papilla of each tubercle, in 
the same manner as the ligamentum teres of the human thigh- 
bone. ‘Transverse slices of the spines exhibit the internal 
structure, and are beautiful objects under the microscope. 
There are also minute appendages to the integument, 
called pedicellarice, or pinchers, of a very remarkable cha- 
racter, whose functions are not known. They are slender 
columnar bodies, each crowned with three calcareous teeth- 
like spines, beautifully sculptured, and which in some species 
are long and slender, in others short and obtuse. I have 
not observed any traces of these bodies, even in the best 
preserved echinites, but as they are as durable as the spines 
and case, they may exist in a fossil state. 
This general view of the structure of the recent Echinites 
will enable the student to understand the nature of the 
fossil remains ; for the parts above described, are found more 
or less perfectly preserved, either in their natural arrange- 
ment, or separated and dispersed in the rock. The habits 
of these animals, of burrowing in the sand, were favourable 
to their preservation in a mineralized state ; and in some of 
the oolitic limestones, hundreds of beautiful examples of 
Turban Echinites (Cidares), having their spines spread out 
on the face of the rock, are found lying in the positions they 
evidently occupied when living. The quarries near Calne and 
Chippenham, in Wilts, are celebrated for such fossils. 
It was my intention to give figures of the genera into 
which the numerous fossil species have been divided by 
