78 ZOOLOGY. 



of granular cords, but Qnoy and Gaimard could not detect these organs. 

 Some authors place this family among the Caryobranchia. 



Order 3. Caryobranchia. 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 fin in swimming. The animal is usually inverted in the water, 

 the foot being above. The branchias are pectinated, and arranged around 

 a nucleus, whence the name of the order. Some of the Ileteropoda of 

 Lamarck belona; here. The order has the additional half Latin and half 

 Greek hybrid name NxicleobrancJiio^ wfeich is inadmissible. 



Fam. 1. Atlantidce. The genus Atlanta has an extremely delicate, 

 vitreous, transparent shell, shaped like planorbis, with the aperture trumpet- 

 shaped, with one side deejily 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 lai-ge, compressed, and provided 

 with a small sucker above. Eyes two, behind the tentacles. This genus 

 is found far at sea, swimming with great lacility, and sinking when not in 

 action. Deshayes thinks the fossil genus Bellerophon is allied to this genua 

 in its natural affinities. 



Fam. 2. Carinarmlcv. The shell of Carinaria is extremely delicate, 

 and nnich smaller than the animal {j^l. 74,^^. 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 {j:)!. 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. 

 branchiae 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 Carinaria^ 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. 



Fam. 3. Pterotracheidw. This family is allied to the preceding one, but 

 ^he 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. 



Fain. 4. PUrosomida. 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 branchite were observed. 

 P. plana is nine centimetres long, and inhabits the sea between the 

 Moluccas and New Guinea. 



Order 4. Gymnobrancuia (also known by the hybrid term of Nudi- 

 h'ancJiia). 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 affijrd 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 disc or 

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