7() GUIDE TO THE FOSSIL INVERTEBIIATE ANIMALS. 
Qallery 
VIII. 
Table-case' 
27 . 
Centre' 
case. 
Gallery 
VIII. 
East Side. 
Other from the soap-stone of Fiji, and they have been held to 
prove that those rocks were raised from <^reat depths since 
the Pliocene Epocli. 
Class HOLOTHURIOIDEA. 
The Sea-eiicnmbers, which form tlie last Class of Echino- 
derma, have no continnous skeleton, and are represented as 
fossils only by the spicules and minute plates depo.sited in 
the skin. These have been found so far hack as in rocks of 
Carboniferous age. Spicules of Cuciimaria from the Pliocene 
beds of St. Erth, Cornwall, and ydates of Psohts from Scotch 
Glacial beds are e.vhibited. 
• 
An nyu’ight case in the middle of the Gallery contains a 
series of specimens intended to illustrate the importance of 
ECHINODERMS as ROCK-FORMERS. The liack, or west 
side, of tlie case contains a single polished slab of IMountain 
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 
blastoids, and of echinoids. The free-moving echinoderrns, 
however, do not form so large a j)roportion of any rock as do 
the fixed forms. The latter often compose masses many feet 
in thickness and affording excellent building-stone. 
The latest comprebensive account of Echinoderma, in- 
cluding fossil forms, is in Volume III. of “Treatise on 
Zoology,” edited by E. Pay Lankester (Loudon, 1900). 
ANNELIDA. 
Among the numerou.s and diversely built forms of life 
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 tliem again it is 
only the Glass CHAETOPODA (bristle-feet) and, witli few 
exceptions, only one Order of that Class, namely the 
Polychaeta (mauy-bristles), with which we have to deal. 
These animals are nearly all marine, and at any rate have 
no representatives among freshwater fossils. They are all 
