the last three divisions of invertebrate animals occupying each an equal de- 

 gree of rank with the vertebrate. 



These four primary divisions of the Animal Kingdom may be subdivided 

 into classes as follows : — 



Sub-kingdom I. VERTEBBATA. 



Class 1 Mammalia Mammals. 



2. Aves Birds. 



3. Reptilia Frogs, Lizards, Tortoises, Snakes &c. 



4. Pisces Fishes. 



Sub-kingdom II. MOLLUSCA. 



Class 1. Cephalopoda Mollusks that walk with their head down- 

 wards. 



2. Gasteropoda That acquire motion by the aid of a con- 



tractile and expansile disk. 



3. Pteropoda That swim by means of a pan of wing-like 



fins. 



4. Lamellibranchiata*. .That have the branchiae, or breathing or- 



gans, in thin plates. 



5. Brachiopoda That are provided with a pan of spirally 



twisted arms. 



Sub-kingdom III. AETICULATA. 



Class 1. Lepades Barnacles. 



2. Anellides Leaches, Earth-worms, &c. 



3. Crustacea Crabs, Lobsters, Shrimps &c. 



4. Arachnida Spiders, Scorpions &c. 



5. Insecta Bees, Beetles, Butterflies, Centipedes &c'. 



Sub-kingdom IV. RADIATA. 



Class 1. Badiaria Sea Eggs, Star Fishes &c. 



2. Polypi Polypes or coral insects. 



3. Entozoa Intestinal Worms. 



4. Infusoria Animalcules. 



* In order to distinguish the classes of Mollusca by an equivalency of terms throughout, I in- 

 troduced in my ' Conchologia Systematica ' the word Tropiopoda in reference to this class, founded 

 on the most prominent form of the foot— the narrow keel-shape ; and it was adopted by Professor 

 Macgillivray of Aberdeen in his Report of the Mollusca of that coast. It has, however, been 

 since demonstrated by Professor Owen, in his Hunterian Lectures, that the foot whose modifi- 

 cations offer so excellent a character for the distinction of classes in the higher orders of Mol- 

 lusca, is not only too variable in its formation and uses for that purpose in the Bivalves, but 

 is sometimes altogether wanting. The lamellated character of the branchia?, or breathing organs, 

 has been preferred, and I now readily adopt it. Although au equivalency of terms is a great assist- 

 ance to the memory, Nature is so variable in her characters that it cannot be embraced to any ex- 

 tent with accuracy. 



