DOSSIL STAR-FISHES AND SEA- URCHINS. 151 



Echinocyamus. In some respects it is a connecting 

 link between the Echini, or sea-urchins, and the 

 "heart-urchins," or Spatangi. The common "sea- 

 egg " (as fishermen call it), or Echinus sphczra, is as 

 old as the Pliocene period, for I found it in the 

 Coralline Crag beds. The common " sea-egg," how- 

 ever, is not the type with which we ought to compare 

 the very abundant " fairy-loaves " (Ananchytes) found 

 so plentifully in the chalk. The mouth and anus of 

 Ananchytes are both at the base, whereas in the sea- 



Fig. 1-24,Micraster, a common Cre- 

 taceous Echinoderm, showing the 

 "petaloid" arrangement of the 

 ambulacral areas. 



Fig. 125. Galerites albogalerus, a 

 common Cretaceous Echinoderm. 



egg they are relatively at the base and the summit. 

 In the Ananchytidce must be included the extinct 

 genera, more or less common in the Chalk, of Holaster, 

 Galerites, etc., in which the basal position of mouth 

 and anus is slightly different. Indeed, the genus 

 Ananchytes appear to be entirely confined to the 

 Cretaceous strata. The nearest living type of sea- 

 urchin, allied to the Ananchytes, or " fairy-loaves," 

 was dredged up in the North Atlantic during the 

 Challenger expedition, from a depth of nearly 



