XXVI SYSTEMATIC INDEX. 



12. Muscle tribe. Have a two-valved shell, and the hinge with- 

 out teeth, but marked with a longitudinal groove .... page 305 



13. Argonaut tribe. Have a single- valved shell, with the spire 

 involute >>> 



14. Cowry tribe. Have a single-valved shell, with a narrow 

 aperture toothed on each side 306 



15. Snail tribe. Have a singled- valved shell, with a regular 

 spire, and the opening somewhat lunate, or crescent- 

 shaped ib. 



ORDER IV. ZOOPHYTES. 



Several of these animals inhabit the same stem, or branches, and 

 altogether appear somewhat like the flowers of plants. 



1 6. Coral tribe. Have a hard and stony or calcareous stem . . 307 



17. Sponge tribe. Have a soft, spongy, flexile stem, capable 



of sucking up water 308 



18. Polype tribe. Have a soft, naked, and fleshy stem .... ib. 



ORDER V. ANIMALCULES. 



These are simple, microscopic animals. 



19. Vorticella tribe Have external organs ; and their body 

 naked and ciliate, or furnished with numerous fibres, at 

 thetip 309 



20. Vibrio tribe. Have no external organs ; and their body 

 round and elongated ib. . 



