76 GUIDE TO THE FOSSIL INVEETEBEATE ANIMALS. 



Gallery other from the soap-stone of Fiji, and they have been held to 

 VIII. prove that those rocks were raised from great depths since 

 the Miocene Epoch. 



Class HOLOTHURIOIDEA. 



The Sea-cucumbers, which form the last Class of Echino- 

 derma, have no continuous skeleton, and are represented as 

 fossils only by the spicules and minute plates deposited in 

 the skin. These have been found so far back as in rocks of 

 Table-case Carboniferous age. Spicules of Cucumaria from the Pliocene 

 27. beds of St. Erth, Cornwall, and plates of Psoitis from Scotch 

 Glacial beds are exhibited. 



Centre- An upright case in the middle of the Gallery contains a 

 case. series of specimens intended to illustrate the importance of 

 ECHmODERMS as ROCK-FORMERS. The back, or west 

 side, of the case contains a single polished slab of Mountain 

 Limestone full of stems and other fragments of Carboniferous 

 crinoids. On the front of the case is a large slab of Silurian 

 limestone from Gotland, with masses of crinoid stems 

 showing on its weathered surface. Above this are samples 

 of rock from various parts of the world, composed entirely or 

 in great part of the skeletons of crinoids, of cystids^ of 

 Mastoids, and of echinoids. The free-moving echinoderms, 

 however, do not form so large a proportion of any rock as do 

 the fixed forms. The latter often compose masses many feet 

 in thickness and affording excellent building-stone. 



The latest comprehensive account of Echinoderma, in- 

 cluding fossil forms, is in Volume III. of "Treatise on 

 Zoology," edited by E. Ray Lankester (London, 1900). 



ANNELIDA. 



Gallery Among the numerous and diversely built forms of life 

 ^■'■^^v, that popular phraseology lumps together as worms, only the 

 ^ ®' segmented or ringed worms have left in the rocks traces that 

 can be identified by the palaeontologist. These worms 

 constitute the group Annelida, and among them again it is 

 only the Class CHAETOPODA (bristle-feet) and, with few 

 exceptions, only one Order of that Class, namely the 

 Polychaeta (many-bristles), with which we have to deal. 

 These animals are nearly all marine, and at any rate have 



