358 Pteropoda. M OLLU SC A. Conchifera. 
Genus Limacina. — T his is the only genus in the 
often mentioned bv them. Peyrfre, in his “ Histoire 
family; the shell is subglobose, with a slightly raised 
du Greenland,” calls it, “ a little black spider.” Martens, 
spire, the last whirl obscurely keeled, and the axis 
in his “Voyage into Spitzbergen and Greenland,” calls 
umbilicated. 
it the “ snail slime fish,” and tells us that they “ swim 
L. ARCTICA is the best known species, and is 
in great numbers in the sea, as numerous as the dust in 
extremely abundant in the North Sea, where it forms 
the sun,” whilst Otho Fabricius, in his “Fauna of 
an important article of food for the whale. It was well 
Greenland,” gives us a full and very interesting descrip- 
known to some of our early arctic voyagers, and is 
tion of it. 
Order II. — G-YMNOSOMATA (Shell-less Pteropods). 
These naked-bodied or Shell-less Pteropods are distin- 
because the lumhs, pigeon-divers, and j^oiret-divers are 
guished from the preceding order by their body being 
plentifully seen in those places where these fish or sea- 
destitute of a shell. It is composed of three families. 
insects are seen.” 
none of them containing more than a few species, and 
very few of these being much known. No douht many 
Family— PNEUMODERMID iE. 
more species will he discovei'ed floating on the seas of 
warm latitudes ; but at present the most interesting are 
The Pneumodermons have a fusiform body, and the 
one or two found in our Northern Ocean. 
head is provided with arms furnished with pedicelled 
suckers. The wings or fins are rounded, entire, with a 
Family— CLIONID^. 
central foot-like appendage placed at the base of the 
head. The gills are placed on the hinder part of the 
The Olios have a fusiform body, furnished with two 
body. There are four genera in this family, each distin- 
fins, and a central foot-like appendage. Their head is 
guished from the other chiefly by the gills. 
furnished with a series of conical prominences on each 
The Genus Pneumodermon has them in the form 
side, which prohahly represent rudimentary tentacles; 
of a four-lobed leaf at the extremity of the body. 
they are retractile, and furnished with numerous micro- 
Spongiobranchia has them in the form of a pro- 
scopic suckers. 
minent spongy ring near the end of the body. 
The Genus Clio {=Clione) is the hest known of the 
Trichocyclus has them in the form of a ciliated 
family, as one of the species belonging to it is a native 
ring round the middle of the body, one round the 
of our arctic seas, and has been frequently observed in 
base of tbe head, and another on the hinder end of the 
its native haunts by our arctic voyagers. 
body. 
THE CLIO BOREALIS is a small, gelatinous, pellucid 
creature of a pale blue colour, with a scarlet mouth and 
Family— CYMODOCEID^. 
extremity. Dr. Scoresby says that it occurs in vast 
numbers in some situations near Spitzbergen. Phipps 
The Cymodoceas have the body divided into two 
remarks — “ Our flshermen call them by the name of 
parts, and are furnished with four wings or fins, the 
‘ Whale-food,’ and are of the same opinion with Mar- 
two upper broad and rounded, the lower nearly linear. 
tens, who says tliey are the chief food of the whalebone- 
The family contains one genus, Cymodocea, and this 
whale.” Martens, in his “ Voyage into Spitzbergen,” 
genus only one species, C. diaphana — a diaphanous. 
tells us that they are called the “ Sea May-flie.” “ I am 
translucent, little creature, with the scarlet viscera 
of opinion,” he says, “ that the birds feed upon them. 
shining through it. It is found in the Alantic Ocean. 
Class IV.— CONCHIFERA (Bivalves). 
The Bivalves come next to the Univalves in variety 
seize upon such particles as the water floats within 
and importance ; and though in the number of species 
their reach, or which are brought near the mouth by 
they are inferior, they exceed them in the number of 
tbe currents that are continually circulating within the 
individuals. They are all aquatic, the greater proper- 
cavity of tbe mantle. These currents not only serve. 
tion being marine, and are widely diffused over the 
but supply water to the gills for aerating the blood ; 
globe, ranging from low water mark to a depth of more 
they are produced by the action of a number of cilia 
than two hundred fathoms. The animals have no dis- 
that clothe the gills. The foot of tbe Bivalves bas 
tinct head — hence called by many naturalists Acepliala, 
some analogy with that organ in the Gasteropods, being 
or beadless — no tentacles, and (in by far the greater num- 
formed by the under part of the body, but is not so 
ber at least) no eyes. The mouth is concealed between 
well adapted for locomotion as in these latter mollusks. 
the folds of their mantle ; it is situated near the front of 
Instead of forming a flattened disc as in them, it is 
the base of the foot, and is provided laterally with two 
generally laterally compressed and keeled — (see fig. 
pairs of elongate fleshy lips, forming lamellar It 
228, Verms verrucosa) — though indeed there are many 
possesses no teeth, and the creatures thus can only 
exceptions to this rule. In the Oyster and Scallop 
