12 
to have been remarked in a mineralised state. C. circinnatus is only 
known as a fossil, and is figured by Rumphius, Amb. PI lix. Fig. c. 
and by Breynius, p. 55, who names it Fchinometra Circinnata. 
The chalk specimen, Plate I. Fig. 10, from Kent, does not suffi- 
ciently agree with any species with which I am acquainted, to allow 
of its being supposed to be exactly analogous. It may, however, be 
considered as belonging to this genus ( variolata.) 
The third genus of Cidaris is C. mammillata. The first species of 
this genus is distinguished by Leske by the name of the genus, and 
figured by Klein, Tab. vi. a. b. c. d. The shell of this species is ellip- 
tical and depressed. The areae are, five large, and as many small, 
beset with papillae, not perforated, and of a size proportioned to the 
areae : the ambulacra are singly porous. This species is not very 
common in a fossil state. The fossil referred to by Leske, in Bourguet, 
Fig. 33/, is certainly of this species ; but that of Lister cannot be 
spoken of so decidedly. 
The next species, C. papillata, Lesk. and E. cidaris, Lin. the 
moorish turban ( cidaris maurij, is round in its circumference, and 
rather depressed. It has five areae, on which are alternately disposed 
two rows of mammillae, each of these being surmounted by a perfo- 
rated papilla, crenulated at its base, and surrounded by a distinct 
groove : the rest of the area being filled by minute puncta and gra- 
nular projections. Each papillary tubercle of this echinus has its own 
plate. Between each pair of ambulacra, which are biporous and un- 
dulating, is a narrow granulated band : these are considered by Leske 
as the less areae. 
Petrified specimens of this species have been frequently figured 
and described. These are, the ova anguini of Pliny, and the brontice 
of Agricola. They are also figured by Plot, Hist, of Oxfordshire, 
Tab. v. Fig. 3, 4 ; and copied by Lister, lap. turb. Fig 22 and 25. 
Lhwydd, Tab. 12, Fig. 910, has depicted a fragment; and Morton, 
two complete specimens, Hist, of Northumberland, Tab. 10, Fig. 3, 5, 
