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MOLLUSCA. 



[Order I. MOLLUSCA CEPHALA.— Head distinct from 

 the body, bearing the lips or jaws. 



Sect. I. NATANTIA. — Organs of progressive motion Jitted 

 for swimming. 



( CEPHALOPODA — Fins in the form of tentacula, surrounding the 

 \ mouth. Marine. 



{Nautilid.*: — With a multilocular shell. 

 Sepiad^e. — Destitute of a multilocular shell. 



.Sect. II. GASTEROPODA. — Organs of progressive motion 

 fitted for creeping. 



I. PULMONIFERA — Respiring in air by means of a single 

 pulmonary cavity. 



Terricola. — Resident on land. 



Aquatic a. — Resident in the water. 



II. BRANCHIFERA Respiring in water. 



Nudibhanchia — Branchiae external, pedunculated, and plu- 

 mose. 



Pectinibranchia. — Branchiae in the form of sessile, pecti- 

 nated ridges, contained in a cavity. 



Order II. MOLLUSCA ACEPH ALA.— 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. 



J Sessilia. One valve of the shell cemented, fixed. 



.II. BIVALVIA — Mouth destitute of spiral fringed arms. 

 Asiphonida. — Cloak open, without syphons. 

 Siphonida — Cloak more or less closed, forming syphons. 



Sect. II. TUNICAT A— Covering soft. 



Dichitonida. — 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. P 



