23 
formation appears to have taken place, by the shell becoming im- 
perfectly invested, both on the in and the outer side, with the pyrites, 
which then obtained a partial covering of drusy quartz ; the acid 
resulting from the decomposition of the pyrites subsequently removing 
the shell, the impressions, which are plainly discernible, showing the 
forms of the plates of the shell, and the sutures by which they were 
joined. That the quartzy incrustation took place previous to the 
removal of the shell, is shown by the spaces which the shell has left 
being left entirely free from crystals. 
The third section of the class of Catocysti is named Scutum by 
Klein, and Echinanthus by Leske and Phelsum. The shells comprised 
under this section are of an irregular figure, resembling an oblong or 
angular buckler. On the base, which is concave, five grooves pass 
from the margin, and terminate at the mouth in the centre. The 
upper part is ornamented with five rays, which have been supposed 
by some to resemble a pentaphylous flower, and by others a five- 
layed star. The mouth, which is pentagonal, is furnished with five 
teeth of an alated form and a plumose appearance, and is placed in the 
centre of the base, the anus being at the margin. The whole of the 
surface is beset with minute circular depressions, with central tubercles. 
One genus, Echinanthus, Lesk. comprises all the shells of this 
section. The first species, Scutum humile, Klein. Tab. xvn. a. 
XV m ; Echinanthus htimilis, Lesk. is rather of an oval form, and 
is divided into ten areae by five biporous, pentaphyloideal ambulacra, 
the five smaller areas being comprised in the pentaphyloid surface 
oimed by the ambulacra, and having grooves pass across them, and 
connecting the immediately opposite pores. Specimens of this species, 
in a mineralized state, are represented by Aldrovandus, Met. Mus. 
p- 499, Fig. 1 : Scilla, Tab. x. Fig. 2, 3 ; Tab. xi. No.’ 2 : Watch, 
Tab. E. Y . Fig. 1 , 2. This species is chiefly found in a petrified state in 
Malta and in Occitania. Dr. Shaw figures a fossil of this species found 
m tlie desert Marah, Voyage to Barhciry, $c. Fig. 40, p. 128, app . 
