266 HISTORICAL PALAZONTOLOGY. 
fectly fitted for preservation in the fossil condition. The corals 
of the Cretaceous series are not very numerous, and for the 
most part are referable to types such as Zvochocyathus, Stephano- 
phyllia, Parasmilia, Synhelia (fig. 190), &c., which belong to 
the same great group of corals as the majority of existing 
ses 
her thee 
7 
ey 
~ a 
eit = ae hm 
i ‘ at 
Q Bom 
Fig. 190.—Synhelia Sharpeana. Chalk, England. 
forms. We have also a few “ Tabulate Corals” (Polytre- 
macis), hardly, if at all, generically separable from very ancient 
forms (/feliolites); and the Lower Greensand has yielded the 
remains of the little Holocystis elegans, long believed to be the 
last of the great Palzeozoic group of the Augosa. 
As regards the Echinoderms, the group of the Crvinotds now 
exhibits a marked decrease in the number and variety of its 
types. The ‘‘stalked” forms are represented by FPentacrinus 
and Bourgueticrinus, and the free forms by Feather-stars like 
our existing Comatule ; whilst a link between the stalked and 
free groups is constituted by the curious “Tortoise Encrinite 
(Marsupites). By far the most abundant Cretaceous Echino- 
derms, however, are Sea-urchins (/chinoids); though several 
Star-fishes are known as well. The remains of Sea-urchins are 
so abundant in various parts of the Cretaceous series, especi- 
ally in the White Chalk, and are often so beautifully preserved, 
that they constitute one of the most marked features of the 
fauna of the period. From the many genera of Sea-urchins 
which occur in strata of this age, it is difficult to select char- 
acteristic types; but the genera Galerifes (fig. 191), Descotdea 
(fig. 192), Micraster, Ananchytes, Diadema, Salenia, and Cv- 
