CEPHALOPODA. 18 



webbed ; tentacles very long, not retractile ; siphon short, without 

 attachment to the head, or valve. Shell or gladins small, long, 

 lance-like. 



Family Thysanoteuthid^. Bod}^ rather long or oval ; mantle 

 supported by cartilaginous ridges and grooves ; arms free ; 

 siphon united to the head by two bands. Gladius dart-like. 



Family Onychoteuthid^. Body long, cylindrical; mantle 

 supported by cartilaginous projections ; eyes with a lachrymal 

 sinus ; arms or tentacles armed with hooks ; siphon with or 

 without bands and valve. Gladius generally lancet-form, with 

 an end-conus. 



Family Ommatostrephid^. Body long, cylindrical ; arms short, 

 armed with suckers only ; the short tentacular arms non-retrac- 

 tile ; siphon valved, united by bands to the head. Shell small, 

 lancet-form, with an end-conus. 

 B. Decapoda calciphora. Internal shell calcareous, 

 a. Sejnophora. Shell blade-like. 



Familj^ Sepiid^. Eyes covered by skin ; littoral. Body oval, 

 with long lateral fins, uniting behind ; mantle supported by carti- 

 laginous tubercles fitting into sockets on the neck and siphon ; 

 arms with suckers, tentacular arms entirely retractile ; siphon 

 valved. Shell (cuttle-bone, sepion or sepiostaire) broad, flat, 

 thickened internally by numerous plates, terminating behind in 

 a hollow, imperfectly chambered apes or mucro, without con- 

 necting siphon. 



b. Phragmophora. Shell foi^niing a series of chambers traversed 



by a siphon. 



Family BELOSEPiiDiE. (Fossil onl}^) Shell like Sepia, but the 

 walls of the chambers of the mucro pierced by small holes, 

 indicating the existence of a connecting siphon. Animal un- 

 known. 



Family Belemnitid^. (Fossil only.) Animal, arms with 

 hooks. Shell a pen (pro-ostracum) attached to a chambered cone 

 (phragmocone), the partitions of which are pierced by a sub- 

 marginal, ventrally-placed siphuncle ; at the hinder end the 

 phragmocone is enveloped by a rostrum. 



Family Spirulid^. Animal, body oblong, with minute ter- 

 minal fins ; mantle supported by a cervical and two ventral 

 ridges and grooves ; arms with six rows of minute cups ; tentacu- 

 lar arms elongated; siphon valved. Shell spiral, whorls on the 

 same plane, not in connection, chambered ; chambers connected 

 by a ventral siphon, invested by a series of cone-shaped tubes, 

 one for each chamber. The shell is placed vertically in the end 

 of the body, and is held in place by side flaps of the mantle. 



The above succession of families indicates a progression from 

 the so-called naked octepods (with the internal shell represented 



