PLATE VI. 



SHELL OF ECHINO-DERMATA, GASTEROPODA, ETC. 



1. Portion of a transverse section of the Spine of an Echinus. 2. Another section, exhibiting reticulated structure, 

 the calcareous portion having been dissolved out by acid. 3. Horizontal section of shell of Hnliotis splendens, 

 with stellate pigment in the interior. 4. Portion of Shell of a Crab, showing granules beneath the articular 

 layer. 5. Another portion of same Shell, showing its hexagonal structure. 6. Horizontal section of Shell 

 of Terebratula rubicunda, showing the radiating perforations. /. Transverse section of shell of Pinna ingens. 

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



