ANANCHYTES OVATUS. 326 
Spatangidee which have the ambulacra depressed, and the 
shell cordiform. The pores of the even ambulacra are 
united by a furrow. The vent is on the posterior face. The 
common chalk Spatangus belongs to this genus. (Lign. 
107.) 
4, Holaster.—The shells are heart-shaped ; the ambulacra 
simple, and converging towards the summit ; the mouth is 
transverse ; the outlet is within the posterior face. 
Anancuytss ovatus. Lign. 104. fig. 2.—These sea urchins 
are among the most characteristic of the fossils of the Upper 
Chalk, and are peculiar to the Cretaceous formation. They 
are readily distinguished by their elevated helmet-like form, 
and by the transverse mouth and oblong outlet situated on 
the inferior face of the flat base, and towards the margin. 
(Lign. 104, fig. 2%.) 
The vernacular names of “ Shepherd’s Crown,” and “Fairy 
Loaf,” indicate the form of these abundant fossils. The 
shell is oval in its longest diameter; flat, or nearly s0, 
below ; and rounded, conical, and somewhat laterally com- 
pressed towards the summit. The ambulacra are five, 
between double lines of pores; the tubercles are minute 
and scattered ; the substance of the shell is of great thick- 
ness. More than twenty species of the genus are known. 
The helmet Echinites, like the preceding, have given rise 
to innumerable siliceous casts, which are found associated 
with those of other forms in the Drift, on the ploughed 
lands, and among the shingle on the sea-shore ; they are 
often placed as ornaments on the mantel-shelves of the 
cottagers. <A flint cast of an Ananchyte, in which the plates 
were partially separated, is represented Lign. 103, jig. 1. 
The shells are sometimes filled with pyrites ; and occasionally 
are found partially empty, with crystals of calc-spar symme- 
trically arranged on the inside of the shell, parallel with the 
rows of ambulacral pores. Lign. 103, jig. 3, is a remarkable 
