( S25 ) 
MOLLUSCA. 
Order I. MOLLUSCA CEPHALA.— Head distinct from 
the body, bearing the lips or jaws. 
r Sect. I. NATANTIA. — Organs of progressive motion fitted 
for swimming. 
f CEPHALOPODA. — Fins in the form of tentaciila, surrounding the 
J I mouth. Marine. 
j NAUTiLiDiE — With a multilocular shell. 
( Sepiad^. — D estitute of a multilocular shell. 
I Sect. II. GASTEROPODA. — Organs of progressive motion 
f tied for creeping. 
r l. PULMONIFERA. — Respiring in air by means of a single 
pulmonary ca\dty. 
^ Terricola — Resident on land. 
I Aquatica — Resident in the water. 
III. BRANCHIFERA. — Respiring in water. 
Nudibranchta — Branchise external, pedunculated, and plu- 
mose. 
Pectinibranchia. — Branchise in the form of sessile, pecti- 
nated ridges, contained in a cavity. 
Order II. MOLLUSCA ACEPHALA.— Destitute of a 
distinct head or neck. 
Sect. I. CONCHIFERA . — Covering testaceous. 
' I. BRACHIOPODA — Mouth with a spiral arm on each side, 
fringed with filaments. 
Pedunculata. Shell supported by a cartilaginous stalk. 
Sessilia. One valve of the shell cemented, fixed. 
HI. BIVALVIA. — Mouth destitute of spiral fringed arms. 
Asiphonida. — Cloak open, without s^'^phons. 
SiPHONiDA — Cloak more or less closed, forming syphons. 
t Sect. II. TUNICAT A.— soft. 
Dichit ON IDA. — Inner tunic detached from the external one, 
and united only at the two orifices. 
MoNOCHiTONiDA.—Inner tunic adhering throughout to the 
external one. 
VOL. I. 
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