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number about twenty-five, are largest near the front of the 
shell; at the sides they are smaller and lic closer together : 
each spine has a dorsal ridge and a distinct furrow beneath. 
Beaks projecting. ‘The whole surface of the shell is covered 
with very fine transverse projecting striz ; the lines of growth 
sometimes interrupt the regularity of the furrows, and the 
spines are sometimes very short and adpressed, at others 
they are irregularly bent, but their general position is at an 
angle of about 45° with the shell. The breadth is rather 
above two-thirds of the length. I can discover no muscular 
impression within the shell, although I have specimens 
perfectly cleared from the chalk. 
_ This species is common both in the soft and hard Chalk, 
and is often attached to Flints. I have received it in hard 
Chalk from Mr. Mantell, found near Lewes; from Norton 
Bevant, Heytesbury, &c. from Miss Benett. Inside casts 
are common in gravel flints, these, of course, do not expose 
the spines. Mrs. Morris sent me a specimen picked up at 
Rickmansworth, and I have a cast in Calcedony, found 
near Sidmouth, for the possession of which I am indebted to 
the kindness of my friend Mr. Thomas. Its varieties are 
almost, nay sometimes quite, destitute of spines; Mr. Man- 
tell sent me a specimen from Lewes, in which some of the 
spines are almost at right angles to the shell, and the others 
laying in bas-relief, curving in elegant turns, as if too weak 
to rise. 
Fig, 1 represents the spinous side of a specimen said to be 
from Brighton, the Chalk is cut from it as far as might be 
to leave support to the spines; the beak of the plain side is 
just visible. Fig. 2 gives the dorsal view of a specimen 
from Northfleet, showing the triangular aperture: this 
specimen had the remains of a Flustra on some parts of it. 
Fig. 3 the inside of a detached spinous valve, having no 
appearance of a muscular impression, as in Pecten. 
