Pteropoda , Gasteropoda , etc. 77 
occur from the close of the Cretaceous period to the base of the 
Secondary rocks ; followed by Geratites in the Trias, and 
Goniatites in the Carboniferous formation, their variations in 
form and in ornament being only modifications of the shells 
of the same family. 
The older forms chiefly belong to the straight Orthoceratites , 
having shells like a Nautilus but uncurled and straightened out, 
or to curious forms, having various degrees of curvature in the 
shell, between the straight Orthoceras and the involute Nautilus 
and Ammonite. These variations are also found in many genera 
of Cephalopod Shells of the Chalk period. A fuller descrip- 
tion of the contents of this Gallery will be given in a small 
separate Guide in preparation, which will be issued as soon as 
the cases are completely arranged. 
Class 2. — Pteropoda (Wing-shells). 
A single Table-case is devoted to this curious division of 
Mollusca, represented at the present day by small oceanic 
animals, whose entire life is passed in the open sea far away 
from any land, swimming by means of two wing-like appen- 
dages, one on each side of the head. The Pteropods had their 
representatives far back in past geological time. 
In the Miocene beds of Bordeaux, Dax, Turin, Sicily, and 
in . the Suffolk Crag, small delicate shells occur, like the 
existing genera — Hyalea , Vaginella, Cuvieria ; whilst in the Car- 
boniferous, Devonian, and Silurian many species are met with, 
as Gonularia, Hyolithes (Theca), &c., which attained a large 
size compared with the minute shells of living members of this 
class. 
Gallery (No. 8 on Plan). — The second of the wide Galleries 
has thirty-two Table-cases, and Wall-cases corresponding 
with Gallery No. 6. In it are placed the remaining groups 
of the Mollusca, viz., the Gasteropoda, the Lamellibranchiata, 
and the Brachiopoda. It also contains the Polyzoa, the Insecta 
and Crustacea, the Annelida, and Echinodermata. 
Class 3.— Gasteropoda (Snails, Whelks, &c.). 
Class 4.— Lamellibranchiata* (Oysters, Cockles, &c.). 
The fossil shells of the above groups occupy the whole of the 
West or left side of this Gallery and a small portion of the East 
or right side. Wall-cases Nos. 1 to 9 contain the Foreign Mol- 
lusca, and Table-cases Nos. 89 to 104 the British specimens of 
the same group. The Gasteropods, or Univalves, are placed 
first in each case, and the Lamellibranchs, or Bivalves, follow 
them. The whole series is subordinatelv arranged in strati- 
# Called also Pelecypodci, by Goldfuss (1820). 
Mollusca. 
Gallery, 
No. 7. 
Cephalo- 
poda. 
Orthoceras. 
Wall-case, 
No. 8. 
Pteropoda. 
Gallery, 
No. 7 
ou Plan. 
Table-case, 
No. 72. 
Gallery, 
No. 8 
on Plan. 
Wall cases. 
Nos. 1 to 9. 
Table-cases 
Nos. 89 to 
104. 
