426 A. E. Verrill — North American Cephalopods. 



pediceled, with horny rims. Body usually elongated, always with 

 lateral fins.* 



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

 pediceled, destitute of horny rings. Body usually short, obtuse, 

 rarely finned. 



Order I.— DECACERA. 



Decapoda Leach, Zool. Miscel., vol. iii, 1817 (t. Gray) [nan Latr., 1806]. 



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



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

 Decacera Blainville, Diet. Soi. Nat., vol. xxii, 1824; Man. Mai., p. 366, 1825. 

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



Body generally rounded and elongated, often acute posteriorly. 

 Ten prehensile arms, bearing suckers or hooks, which are pediceled. 

 Four pairs of these, called sessile arms, are tapered from the base 

 and covered with rows of suckers along the whole length of the 

 inner face ; the fifth pair of arms, known as tentacular arras, differ 

 from the rest, and arise frona a pair of pits or pouches, situated be- 

 tween and inside the bases of the third and fourth pairs of sessile 

 arms; they have a more or less slender and contractile peduncular 

 portion and a distal, usually enlarged, sucker-bearing portion. Beak 

 protractile, surrounded by an inner, and a loose outer buccal mem- 

 brane, the latter usually with seven or eight angles, united to the 

 arms by membranes. Eyes movable in the sockets, with or without 

 lids. Head united to the mantle either by a dorsal commissure and 

 two lateral, free, connective cartilages ; by three free connective carti- 

 lages ; or by three muscular commissures. Mantle usually supported 

 by an internal, dorsal, horny ' pen,' or by a calcareous, internal, 

 dorsal shell or 'bone;' sometimes the pen is absent; always with 

 muscular fins on each side. Male, when adult, usually with one or 

 two of the arms hectocotylized. 



This group was divided by D'Orbigny into the following two 

 tribes, which are more convenient than natural : 



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

 without an anterior sinus; pupils round. 



MyopsldcB. — Eyes usually covered by transparent skin, sometimes 

 with a thickened fold, forming a lower lid, but in IStoloteuthis the 

 lids are entirely free ; pupils crescent-shaped, rarely round. 



* The name Decacera, though not in so general use as Decapoda for this group, is re- 

 tained because the latter was previously, and still is, in use for a group of Crustacea, 

 and, therefore, cannot properly be used for these Cephalopoda. 



