CEPHALOPODA. 1] 
openings between the pieces of the cowrie, when it is drawn 
up into the canoe and secured.—Lowell’s Edible Mollusks, 167. 
Most of the species of octopods and the Nautilus are littoral 
in habit, and have thence been conjectured to enjoy but a limited 
distribution ; and this is held to justify the multiplication of 
specific names. This reasoning is, however, fallacious, as it is 
well known that many littoral mollusks, not nearly so well pro- 
vided as these with the means of swimming, have become world- 
wide in distribution. So many particular species of Octopus are 
known to inhabit the shores of distant countries, that a large 
proportion of the species which have been distinguished by slight 
and mutable characters, and by their geographical distribution, 
will probably need to be united when sufliciently studied. This 
probable extensive distribution of living littoral species corres- 
ponds with observations made upon fossil species of Ammonites, 
Nautilus and other chambered genera, which are proved to have 
been littoral in habit by their occurrence only in deposits repre- 
senting ancient sea-shores. Not to multiply examples amongst 
these fossils, it may be mentioned that Nautilus simplex occurs 
in Europe, East Indies and Texas ; that Ammonites Rotomagensis 
is found in Europe, East Indies, N.and 8. Africa and 8. America ; 
and that Baculites anceps had even a wider distribution. Never- 
theless, temperature has been observed to have some effect upon 
the distribution of the living Octopoda of Europe, similar but 
distinguishable forms or species inhabiting its northern seas, 
from those of the Mediterranean. As in Molluscan life generally, 
the development of specific forms has been greatest in tropical 
waters. 
It is altogether probable that the pelagic cephalopods, highly 
organized, with powerful locomotive apparatus, and frequently 
attaining great size and strength, may enjoy a distribution fully 
equal to that of the littoral species: such is known to be the 
case in some species which, normally circumboreal in distribu- 
tion, are found nevertheless extending into temperate latitudes 
in both oceans. 

Order 1. DiprAncutaTa.—Breathing by a single pair of internal 
symmetrical branchie or gills. Eyes sessile. Mandibles horny. 
Arms, eight or ten, furnished with rows of acetabulee or suckers. 
Body sometimes laterally or posteriorly finned. Shell internal, 
or none. 
Order 2. TETRABRANCHIATA.—Breathing by two pairs of sym- 
metrical branchiz. Eyes pedunculated. Mandibles shelly. Arms 
yery numerous, without suckers. Shell external, chambered ; 
capable of containing the animal, 
