78 ZOOLOGY. 
of granular cords, but Quoy and Gaimard could not detect these organs. 
Some authors place this family among the Caryobranchia. 
OrvER 3. CaryoprancuiA. The body is gelatinous, transparent, and 
capable of being enlarged by absorbing water. The head is proboscidiform ; 
the foot is long, compressed, or vertical, provided with a little sucker, and 
used as a fininswimming. The animal is usually inverted in the water, 
the foot being above. The branchiz are pectinated, and arranged around 
a nucleus, whence the name of the order. Some of the Heteropoda of 
Lamarck belong here. The order has the additional half Latin and half 
Greek hybrid name Vucleobranchia, which is inadmissible. | 
Fam. 1. Atlantide. The genus Atlanta has an extremely delicate, 
vitreous, transparent shell, shaped like planorbis, with the aperture trumpet-. 
shaped, with one side deeply excised, and having a closely fitting operculum, 
of the same texture as the shell, the spire projecting from one side. The 
mollusc is spiral and compressed, the foot large, compressed, and provided 
with a small sucker above. Eyes two, behind the tentacles. This genus 
is found far at sea, swimming with great facility, and sinking when not in 
action. Deshayes thinks the fossil genus Bellerophon is allied to this genus 
in its natural affinities. 
Fam. 2. Carinarude. The shell of Carinaria is extremely delicate, 
' and much smaller than the animal (pl. 74, fig. 17, on the right hand below). 
Its resemblance in form, and in having a single chamber, induced some ~ 
authors formerly to place it near Argonauta (pl. 76, fig. 17), with which 
the animal has no affinity. The mollusc is gelatinous, transparent, and 
rough ; the eyes two, situated at the base of the tentacles. The heart and 
branchiz are contained in the shell, and opposite to this is the compressed 
foot (or ventral fin), the posterior extremity being provided with another 
fin. The Carinariz are found at sea, and are supposed to feed upon minute 
crustacea. They can attach themselves to floating bodies with the aid of 
the sucker upon the foot. , 
Fom. 3. Pterotracheide. This family is allied to the preceding one, but 
the tentacles and shell are wanting. The former are reduced to tubercles 
(or entirely absent) with the eyes on the outside of their base. A mem- 
brane supplies the place of the shell of Carinaria. Pterotrachea (also named 
Firola) is the principal genus. The habits are identical with those of 
Carinaria. 
Fam. 4. Pterosonide. Composed of the genus Pterosoma, in which the 
body is cylindrical, surrounded horizontally with a broad marginal mem- 
brane used in swimming. Neither tentacles nor branchiz were observed. 
P. plana is nine centimetres long, and inhabits the sea between the 
Moluccas and New Guinea. 
Orper 4. Gymnoprancuia (also known by the hybrid term of Vudi- 
branchia). 'The members of this family are without a shell or a branchial 
cavity, the organs of respiration are in the form of external appendages 
upon the back, and their distribution and shape afford characters for the 
families. The embryonic young have a shell, and they remind us somewhat 
of Atlanta. These animals are monoicous; they have a large flat dise or 
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