64 Dr. T. Wright on Fossil Echinoderms 
have dedicated this species to the Earl Ducie, who collected the 
beautiful specimens we have figured. 
Family CrypeastTRIpZ. 
This natural family includes all the Urchins which have a 
circular, elliptical, or pentagonal form, with a thick test, the 
surface of which is closely covered with small, nearly equal- 
sized tubercles sunken in the plates, and surrounded by ring- 
like areolas ; these all carry short hair-like spines. The mouth 
_,, 18 large, central and pentagonal, and is armed with five strong 
jaws which carry the same number of teeth: the anus is pos- 
® terior, and marginal or inframarginal: the interior of the test 
~ is sometimes divided by pillar-like processes of the inner layer 
of the plates. The dorsal portions of the ambulacral areas have 
a petaloid form, circumscribed by large poriferous zones; the 
basal portions are narrow, rectilineal, or branched. The five 
genital plates form a circle around the madreporiform body, 
and between these are wedged the five ocular plates. This 
family includes the genera Clypeaster, Lamk., Laganum, Klein, 
Echinarachnius, Van Phels., Arachnoides, Klein, Scutella, Lamk., 
Dendraster, Agass., Lobophora, Agass., Encope, Agass., Rotula, 
Klein, Mellita, Klein, Runa, Agass., Moulinsia, Agass., Scutellina, 
Agass., Echinocyamus, Van Phels., Fibularia, Lamk., Lenita, 
Desor. 
Genus Crypraster (Lamarck, 1816). 
Form oyal, inclining to pentagonal, rostrated before, truncated 
behind ; upper surface more or less inflated, sometimes campa- 
nulate, conical or subconical ; inferior surface flat, always concave 
around the mouth, with five straight simple ambulacral furrows 
proceeding from the angles of the mouth to the border; the 
dorsal portion of the ambulacral largely petaloid, greatly exceed- 
ing the interambulacra in size, and forming elegant leaf-like 
expansions, in general convex, arched, and prominent ; bounded 
on each side by large poriferous zones, the pores of which are 
wide apart and united by transverse sulci ; the apical disc formed 
of five genital plates at the summits of the interambulacra, with 
five ocular plates alternating with them; in the centre of this 
circle is the spongy madreporiform body, of a pentagonal figure : 
tubercles uniform in size and very numerous, equally distributed 
over the test; summits perforated, and surrounded by very 
deep areolas ; mouth symmetrical, central, pentagonal, lodged in 
a concave depression in the middle of the base ; auricles composed 
of ten distinct auricular processes set in pairs: the jaws form ~ 
a pentagonal pyramid, composed of ten separate pieces, trun- 
cated at the summit, which is bordered by a subcireular band ; 
