426 
A. E. Verrill — North American Cephalopoda. 
pediceled, with horny rims. Body usually elongated, always with 
lateral fins.* 
Octopoda. — Having only tlie 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) [non Latr., 1806], 
H. & A. Adams, Genera, vol. i, p. 25. 
D’Orbigny. Tabl. Meth. des Cephal., p. 57. 1826; Hist. Cuba, Moll., p. 30, 1853. 
Decacera Blainville, Diet. Sci. 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 arms, differ 
from the rest, and arise from 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. 
Myopsidce. — Eyes usually covered by transparent skin, sometimes 
with a thickened fold, forming a lower lid, but in titoloteuthis 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. 
