1 
326 THE MEDALS OF CREATION. Cuap. IX. | 
shire, and Oxfordshire, and must be familiar to collectors. 
The shell is circular, and much depressed; and has five — 
_ petaloid ambulacra: the odd interambulacral area forms a — 
deep furrow in which the outlet is situated: the mouth is 
median, pentagonal, and surrounded by a strong margin. 
The coloured figures in Pict. Atlas, pl. liv. will enable the 
student to recognize these fossils without difficulty. Splendid 
specimens of an allied form (Clypeaster) occur in the tertiary 
limestone of Malta, (Pict. Atlas, pl. lvi. fig. 7,) and are not 
uncommon in collections. 
Nucteouites (Wond. p. 328).— There is a small type 
belonging to this family, of which several species are so 
abundant in the Oolite, Greensand, and Chalk-marl, that a 
brief notice of their characters may be useful. The shell is 
oblong and inflated, rounded in front and flat behind. The 
pores are united by grooves ; the outlet is in a deep furrow — 
on the superior face ; the mouth is sub-central. One species 
occurs in the Tertiary strata, and there is a recent species — 
inhabits the seas of Australia. There are coloured figures of 
Nucleolites in Pict. Atlas, pl. liv. fig. 5, pl. lv. figs. 6, 8. 
SPATANGID #.—In this tribe of echinites, the case is oblong 
or cordiform. The mouth, elongated transversely and desti- — 
tute of proper jaws, is situated in front of the centre of the 
~~. = 
base, near the anterior border of the periphery. The outlet 
is towards the posterior margin. The tubercles and spines — 
are very small. Four subdivisions are established, namely,— ~ 
1. Ananchytes.—A thick and oval shell; the ambulacra — 
simple and converging towards the summit; the mouth — 
transverse ; the outlet is situated on the inferior face. (Lign. — 
104, fig. 2.) 
2. Spatangus. —This name is now restricted to those 
Spatangide in which the ambulacra are petaloid, the external — 
row of pores slightly elongated, and the inner rows round. 
3. Micraster.—By this term are now distinguished the 
