78 
NATURAL HISTORY. [NEW BUILDING. 
Somateria. 148. 
Branta. 149. 
Fuligula. 149. 
Nyroea. 149. 
Clangula. 149. 
Harelda. 150. 
e. Erismatura. 150. 
f. Mergus. 151. 
Fam. 2. Colymbidce . 152 
to 153. 
a. Colymbus. 152. 
b. Podiceps. 153. 
Fam. 3. Alcadce. 154, 
155. 
a. Alca. 154. 
Utamania. 154. 
Fratercula. 154. 
b. Uria. 155. 
Grylle. 155. 
Mergulus. 155. 
Fam 4. Laridce. 156 to 
161. 
a. Puffinus. 156. 
Thalassidromus. 
156. 
^-Rocellarie. 156. 
b. Catarracta. 158. 
Stercorarius. 158. 
Lams. 158 to 160. 
Laroides. 160. 
Xema. 160. 
Chroicocephalus. 
160. 
Rissa. 160. 
Gavia. 160. 
c. Gelichelidon. 161, 
Tbalasseus. 161. 
Sylochelidon. 161, 
Sterna. 161. 
Sternula. 161. 
Anous. 161. 
Megalopterus. 
161. 
Fam. 5. Pelecanidce. 
162 to 166. 
Sula. 162. 
Pkalacrocorax. 
165. 
The larger Table Cases contain the collection of the 
Shells of Molluscous Animals (in progress of arrange¬ 
ment). Shells are the hard bodies which are secreted for 
their protection by the surface of certain soft inarticulated 
animals, (called Mollusca;) they are generally large enough 
to cover the whole of the body, but some are so small as 
only to protect the more important organs, as the heart, 
lungs, &c. The shell is formed on the animal before it is 
excluded from the egg, and even before the unhatched 
animal has gained all its organs; and a few kinds, as 
the Dorides, &c., which are destitute of the shell in their 
adult state, at which period they are covered only with a 
cartilaginous skin, have a shell to cover their soft and just 
hatched bodies. 
The animals which form these shells constitute a par¬ 
ticular division of the animal kingdom, which, from their 
being soft, fleshy, and destitute of any bony skeleton sup¬ 
porting jointed limbs, or of any hard ringed skin, have been 
called Mollusca. They are covered with a muscular coat, 
called the mantle , endued with a glairy humour, and are 
generally of an elongate form ; walking, or rather gliding, 
on a single central foot or disk, and usually furnished 
with one or more pairs of organs on the head and sides, 
to assist them to move from place to place ; but their most 
distinctive character is, that their nervous system consists 
of a certain number of medullary masses, or ganglions, 
distributing fibres to different parts of the body; one of 
