INVERTEBRATE ANIMALS. 56 



in the lower Oolite, attain their maximum in the Chalk, 

 diminish progressively in the Eocene and Miocene, 

 whilst the living representatives are confined to two or 

 three species found in tropical seas. Estimated number 

 of species : recent, 18 ; British, ; fossil, 285. 



1[ Examples of Rotida, Encope, Pygorhynchus, &c. 



Group 153.— Family SPATANGIDiE. o-Trarayyoc, a sea- 

 urchin. The Spatangidse, or Heart-urchins, live in 

 sand or mud, with which when opened their intestines 

 are found to be filled ; these substances seem to have 

 been swallowed for the sake of the animal matter mixed 

 up with them. Estimated number of species : recent, 

 33 ; British, 4 ; fossil, 176. From the Chalk upwards. 

 II Examples of Meoma, Desoria, Xanthohrissus, 

 Triiiylus, Plagionotus, Sckizaster, Klemia. 



Group 154. — Sub-Class HOLOTHUROIDA. 6\okvpiov, 

 Greek name for the animal. Many links are missing 

 between the Sea-urchins and the Sea-cucumbers, Holo- 

 thuridcB. The latter are worm-like animals, possessing a 

 tough flexible skin, and bearing around the mouth a five- 

 rayed coronal of feathery tentacles. The order includes 

 two families : I. Synaptidce, simple in form, and moving 

 by means of anchor-shaped spicules attached to papillae 

 or minute warts. II. Holothuridce, several species of 

 which are known in commerce as Beche-de-mer or 

 Trepang, used in China as turtle is used in this country. 

 Estimated number of species : recent, 97 : British, 15. 

 ^ Examples of Trepang as prepared by Malays for 

 the Chinese market. Coloured drawings of 

 some of the species, and of their internal 

 anatomy. Specimens preserved in liquid. 



