[75] CEPHALOPODS OF NORTHEASTERN COAST OF AMERICA. 285 



This subclass includes two very natural divisions : 



Decacera. — Having inside the circle of eight sessile arms, two long ten- 

 tacular arms, with suckers or hooks on the distal portion. Suckers ped- 

 iceled, and with horny rims. Body elongated, always with lateral fins. 



Octopoda. — Having only the eight sessile arms. Suckers not pedi- 

 celed, and destitute of horny rings. Body rounded, rarely finned. 



Order I— DECACERA, or DECAPODA. 



Decapoda Leacb, Zool. Miscel., vol. iii (t. Gray) 1817 (non Latr., 1806). 



Hi & A. Adams, Genera, vol. i, p. 25. 



D'Orbigny, Tabl. M6th. des Cephal., p. 57, 1826; Hist. Cuba, Moll., p. 30, 1853. 

 Decacera Blaiuville, Diet. Sci. Nat., vol. xxii, 1824 ; Man. Mai., p. 366, is-j;">. 

 Sepltinia Gray, Catal. Brit. Mus., Moll., vol. i, p. 35, 1849. 



Body generally elongated, often acute posteriorly. Head furnished 

 with ten prehensile arms, bearing pediceled suckers or hooks. Four 

 pairs of arms are shorter, tapering from the base, and covered with 

 rows of suckers along the whole length of the inner face ; the fifth pair 

 of arms, known as tentacles or tentacular arms, differing from the rest, 

 and arising from a pair of pits or pouches, are situated between and in- 

 side the bases of the third and fourth pairs of sessile arms, and have a 

 long and more or less slender and contractile peduncular portion and a 

 terminal, usually enlarged, sucker-bearing portion. Beak at the end of 

 a protractile pharynx, surrounded with a loose outer buccal membrane, 

 which is usually seven-angled and united to the arms by bridles. Siphon 

 usually with an internal valve. Eyes movable in the sockets, with or 

 without lids. Ears behind the eyes. Head united to the mantle either 

 by a dorsal and two lateral, free, connective cartilages or by three mus- 

 cular commissures. Mantle cylindrical or conical, supported by an in- 

 ternal dorsal, horny 'pen,' or by a calcareous internal dorsal shell or 

 'bone;' always with muscular fins along each side, which are usually 

 united posteriorly. Male with one or more of the arms hectocotylized. 



This group has been divided by D'Orbigny into the following two* 

 tribes, which are, perhaps, more convenient than natural : 



Oigopsidcv. — Eyes naked in front, furnished with free lids, with or 

 without an anterior sinus; pupils circular. 



Myopsidce. — Eyes covered by transparent skin, sometimes with a thick- 

 ened fold, forming a lower lid ; pupils crescent-shaped. 



0IG0PSID.E. 

 Family TEUTHIDiE Owen (restricted). 



TeutMdee (})ars) Owen, Trans. Zool. Soc. London, vol. ii, 1838. 



Teivihida; (pars) D'Orbigny, Cephal. Ac6tab., p. xxxvii (Introduction), p. 328, 1835-'48.. 

 Onychoteutkidw (pars) Gray, Catal. Brit. Mus., Moll., vol. i, p. 45, 1849. 

 H. & A. Adams, Genera, vol. i, p. 30. 



Tentacular arms furnished with sharp horny claws or hooks, which 

 correspond with peculiarly and highly modified sucker-rings; true den- 



