55 



542 HISTORY OF SYSTEMS. 



Family 1. Octocera, with 8 tentacular appendages; the 

 rim of the suckers muscular. 



,, 2. Decacera, with 10 tentacular appendages, 2 



eccentric and longer ; the rim of the suckers spinous. 



Order II. Cellulacea. Blainville remarks that it is very 



probable that the animals which form the shells of this 



order are very different from those of the Spirula and 



Argonauta. 



Family 1. Spherulacea. Shell more or less spherical. 

 „ 2. Planulacea. Shell very depressed, not 

 spiral, chambered, with septa visible on the exterior. 

 „ 3. Nummulacea. Shell discoid or lenticular, 

 the whorls concealed, cellular, without a siphon. 

 Order III. Polythalamacea. Ex. Nautilus, Spirula. 



Family 1. Ortiiocerata. Shell conical or slightly 

 compressed, straight or somewhat arched, the septa 

 sinuous or simple, perforated with a siphon. 

 ,, 2. Lituacea. Ex. Spirula. 

 ,, 3. Cristacea. 



4. Ammonacea. Ex. Ammonites. 



5. Nautilacea. Ex. Nautilus. 

 ,, 6. Turbinacea. 



„ 7. turriculacea. 



Class II. PARACEPHALOPHORA. Gasteropoda. 



Sub-class I. P. dioica. 

 Sexes separate, the male and female distinct individuals. 

 Section I. Respiratory organs, and the shell non-symmetri- 

 cal ; the shell almost invariably revolving in spiral from left 

 to right. 



Order I. Siphonobranchiata. Organs of respiration 

 formed by one or two comb-like branchiae situated 

 obliquely on the anterior part of the back, and con- 

 tained in a cavity having its upper wall prolonged into 

 a canal more or less elongated and attached to the 

 columella. 



Family 1. Siphonostomata = Murex, Lin. 

 „ 2. Entomostomata = Buccinum, Lin. 

 ,, 3. Angyostomata. *An ojjerculum. Ex. 

 Strombus, Conus. ** No operculum. Ex. Tere- 

 bellum, Oliva, Voluta, Cyprsea. 

 Order II. Asiphonobranchiata. Organs of respiration 

 formed by one or two comb-like branchiae situated 

 obliquely on the anterior part of the back, and con- 



