CEPHALOPODA.. 651 



Order DIBRANCHIATA. 



With two gills ; an ink-bladder. Shell commonly internal and 

 rudimentary. 



Tribe Decapoda. 

 Family SpirulidcB. Shell chiefly internal, nacreous ; whorls sepa- 

 rate, chambered ; siphon near the concavity of the shell- 

 curve. 



Genus Spirula. 



Family Belemnitidm. Shell internal, consisting of a " phragmocone " 

 with a marginal siphon, lodged in a *' guard," sometimes 

 produced into a horny plate or " pen." 

 Genera Belemnites^ Belemnitella, Belemnoteuthis, Conoteuthis. 



Family SepiadtE. Shell internal, consisting of a flattened " phrag- 

 mocone," lodged in an open " guard," prolonged behind into 

 a " mucro." 

 Genera Sepia, Beloptera, Belemnosis. 



Family Teuthidce. Shell internal, simple, wholly or in great part 



horny, called " gladius " or " pen." 



Genera Coccoteuthis, Enoploteuthis, Onychoteuthis, Histioteuthis, 



CheiroteuthiSj Loligo, Loligopsis, Cranchia, Rossia, 



Sepiola, Sepioteuthis, LeptoteuthiSf Geoteuthis, Belo- 



teiithis. 



Tribe Octopoda. 



Family Pinnata. Shell rudimental, internal, uncalcified : a pair of 

 pallial fins. 

 Genera SciadephoruSy Pinnoctopus, 



Family Nuda. Shell rudimental, internal, uncalcified. No pallial 

 fins. 

 Genera Octopus, Tremoctopus, Eledone. 



Family Testacea. Shell calcareous, simple, external, peculiar to the 

 female. No pallial fins. 

 Genus Argonauta, 



