GEOLOGY. 



69 



British specimens too large for the Table-cases are arranged on the 

 top shelf of the Wall-cases. Attention is directed to Table-case 

 No. 80, in which is exhibited a beautiful series of Trilobites from the 

 Wenlock shale and limestone near Dudley. Many of these Silurian 

 Crustaceans are remarkable for great beauty and variety of form, and 

 exhibit, in some instances (as in Phacops), the singular compound 

 eyes ; and in Encrinurus, the eyes placed upon long eyestalks. 



The largest of the British Trilobites (Paradoxides) exceeds 2 feet 

 in length (see Wall-case No. 14b), whilst the nearly-allied genus 

 Pterygotus, from the Old Bed Sandstone of Forfarshire, measured 

 fully 5 feet in length (see Wall-case 13). 



Division C. Annulosa (Ringed animals). 



Class 1. Annelida (ex. Earth-worms, Sand-worms, Tube-worms, &c). 

 — Sea-worms (Table-case 79 and W T all-case 15), being soft-bodied 

 animals, are seldom preserved in a fossil state ; but their existence is 

 proved by the tracks, burrows, and worm-castings which they have 

 left on the wet mud, and upon the ripple-marked sands of the old sea- 

 shores, before these had become hardened into shales and sandstones ; 

 their microscopic teeth have also been found in a fossil state in the 

 Lower Palseozoic rocks. Some species form shelly tubes,* and these 

 are frequently found in a fossil state in rocks both of Palaeozoic and 

 Secondary age. 



Division D. Echinodermata (Spiny-skinned Animals.) 



1. Echinoidea (Sea-urchins, 



Cidaris). 

 9. Asteroidea (Star-fishes). 

 3. Ophiuroidea (Brittle-stars). 



4. Crinoidea (Stone-lilies). 



5. Cystoidea. 



6. Blastoidea. 



7 . Holothuroidea (Sea-cucumbers). 



The animals grouped in this division are very different in appear- 

 ance, but agree in having their soft parts enclosed within a more or 

 less solid calcareous covering, composed of numerous plates, disposed 

 usually in a distinctly radial arrangement. 



1. This radial structure is particularly observable in the Sea-urchins 

 {Echinoidea), whose tests, of marvellous beauty and variety of form, 

 are, when living, covered with rows of movable spines, which serve 

 as defences, and aid the ambulacral tubes or suckers in locomotion. 

 The spines, which are calcareous, vary greatly in length and form, 

 being often very minute, but sometimes of great thickness, or of 

 extraordinary length. (Many examples of these are exhibited.) 

 Some of the largest of the fossil Sea-urchins, called Clypeaster, are 

 from the quarries of Mokattam, near Cairo, whence the Nummulitic 

 Stone, used in constructing the Pyramids, was quarried (Wall-case 

 15). The Echinoderms of our own Chalk and Oolite are placed in 

 Table-cases 76-78. 



2. Of the Star-fishes the magnificent series of Goniasters and 



* These worms are called " Tubicolar Annelides," or Tube-worms. 



