PLATE VI. 



SHELL OF ECHINO-DERMATA, GASTEEOPODA, ETC. 



1 Portion of • trannverse section of the Spine of an Echinus. 2. Another section, exhibitinB relieulatcd strncturc, 

 lheSl?a?e?u« nSn Sne been dissolved out by acid. 3. Horizontal section of sheirpf H«liolls siileudcns, 

 ilfh Site oKnt in the interior. 4. Portion of Shell of a Crab, showing granules bencoth the arncnlsr 

 wSr 5 A^otlS?BOrtion of same Shell, showing its hexagonal structure. 6. Horizontal sectjon of Shell 

 o/TCTebraVula S?J"drshowing the raiating perforations. 7. Transverse section of shell of Pinna ingcns. 

 8. Costal" of Carbonate of Lime, from the outer brown shell of the oyster. 



