14 
THE ZOOLOGICAL DEPARTMENT. 
[UPPER 
niany-valved Chitons, which have a series of eight shelly pieces or 
" valves " down the back of the animal. 
Tables 25-30. The Heterobranchous Gasteropods, with variously- 
formed respiratory organs. The Bullada? are placed here, and their 
curious strong gizzards ; the Bubble shells, the Aplysia or Sea Hare, 
which feeds on sea-weeds and discharges a deep purple fluid when 
danger approaches ; the Helicidse, or Snails and other allied families, 
which live on land and have cylindrical retractile tentacles. 
Tables 31-48. The Bivalve shells or Conchifera; the animal 
of these is enclosed between two shelly valves, united by a liga- 
ment. Tables 31-38 contain the Siphonophora, which have the 
mantle closed behind, and furnished with two apertures, the lower for 
the admission, and the upper for the emission, of the water from the 
mantle cavity. Some of these, as the Veneridse and other families, 
crawl on a compressed foot, while the Cockles have an elongated foot, 
angularly bent in the middle, and fitted for leaping. Near these, but 
with a small rudimentary byssiferous foot, are the Tridacnse, one of 
which (the T. gigas), when full grown, is the largest and heaviest of 
shells, some of them weighing more than 300 pounds. The Phola- 
dacea, or Boring shells, live sunk perpendicularly in holes in rocks, or 
in sand. Tables 39-48 contain the Asiphonophora, which have the 
mantle-leaves free, and sometimes a separate single siphonal opening, 
for the emission of the water, as the Mussels and Oysters, many of 
which secrete pearls ; the brightly-coloured Spondyli, or " Thorny 
Oysters," with their rough, foliated or spiny shells, and the thin 
Placunse, or " Cake-Oysters," which are semi-transparent. In Table 
49 are shells of the Mollusca which have no distinct foot on the 
under side of the body, and which either live attached to marine 
bodies (Brachiopoda), or float on the surface of the sea (Pteropoda), 
or walk on their heads (Cephalopoda). The Pteropoda have an ex- 
panded fin on each side of the small foot, and float on the surface 
of the sea, especially in the evening. Of these the Limacina and 
Clio, abundant in the Arctic Seas, form a great part of the food 
of the whale. Table 50 contains the shells of Cephalopods; the 
animals (of which the Cuttle-fish is an example) have eight, ten, 
or many strong and elongated arms round the mouth of their 
large and distinct head, on which they crawl : the mouth is armed 
with large beak-like jaws. Their eyes are large, and their back is 
generally supported with a horny blade, sometimes strengthened with a 
shelly coat, as the cuttle bone. They have a secretion of a deep black 
colour, which they emit when in danger, and thus conceal themselves. 
They are very voracious creatures. The female of the Paper Nau- 
tilus (Argonauta) fabricates a delicate symmetrical shell, in which 
she lays her eggs, and there protects them. Both sexes of the Pearly 
Nautilus form a shell for their protection, one portion of which is di- 
vided into chambers. Some of the extinct chambered shells, as the 
Ammonite, are placed with the Nautilus Shell in Table 50. 
In some of the side Table Cases there are — a series of specimens ex- 
