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. VERTEBEATA. 



Class 1 Mammalia Mammals. 



2. AvES Bu-ds. 



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



4. Pisces Eishes. 



Sub-kingdom II. MOLLUSCA. 



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

 wards. 

 3. Gasteropoda That acquire motion by the aitl of a con- 

 tractile and expansde disk. 



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



fins. 



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



gans, in thin plates. 



5. Brachiopoda That are provided with a pair of sphally 



twisted arms. 



Sub-kingdom III. AETICULATA. 



Class 1. Lepades Barnacles. 



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



3. Crustacea Crabs, Lobsters, Slu-imps &c. 



4. Arachnida Spiders, Scorpions &c. 



5. Insecta Bees, Beetles, Butterflies, Centipedes Sec. 



Sub-kingdom IV. EADIATA. 



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



2. Polypi Polypes or coral insects. 



3. Entozoa Intestinal Worms. 



4. Infusoria Animalcules. 



* lu order to distinguish the classes of Mollusca by au equivalency of terms thi'oughout, I in- 

 troduced iu my ' Couchologia Systematica ' the word Tropiopoda in reference to this class, foimded 

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

 Macgillivi-ay 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 an equivalency of terms is a great assist- 

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

 tent with accui'acy. 



