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floating substances. The Heteropods are found on the high seas in every warm 

 part of the globe. They have distinct sexes, are predatory in their habits, feeding 

 upon all sorts of pelagic life which surrounds them. They have no jaws, but are 

 furnished with a radula with seven rows of teeth like the taenioglossate gastropods. 

 Some have shells capable of containing the retracted animal; in others, the shell 

 only serves the purpose of protecting the vital organs, and in some forms it is 

 altogether wanting. The Heteropods may be divided into two families, Ptero- 

 tracheidce and Atlantidce . The former includes the genera Pterotrachca, Firo- 

 loida, Cardiapoda, Carinaria, and Pterosoma; a species of the typical genus 

 being shown on the preceding page. It is a transparent gelatinous creature. 

 The gills are exposed near the tail, and the fin-like foot, with the minute sucker 

 upon the edge, is seen on the opposite side. The sucker is smaller in the fe- 

 males than the males. About sixteen species are more or less determinable. 

 Firoloida has no gill and the visceral nucleus is situated at the posterior end 

 of the body, with scarcely any caudal prolongation beyond it. The males are 

 provided with two slender tentacles in front of the eyes, the females being without 



these appendages, and the fin sucker, 

 as in Pterotrachea , is also larger in 

 the males. Neither this genus nor 

 the preceding has any shell. In the 

 allied Cardiapoda the nucleus is 

 pedunculated, and partly protected 

 by a minute glassy spiral shell. The 

 most interesting of this family is 

 Carinaria, on account of its beauti- 

 ful vitreous cap-shaped shell; the 

 animal being rather like that of 

 Cardiopoda. The commonest species 

 is the well-known Mediterranean 

 C. lamarcki, but the largest is C. 

 cristata from the Indian and China 

 seas. The embryonic shell of 

 Carinaria is spirally coiled like a 

 snail shell, and bears no resemblance 

 to the beautiful adult structure. The 

 latter at one time was so rare that 

 five hundred dollars is said to have 

 been given for a specimen. Even 

 -now, large and perfect shells are rare. The Atlantidce contains two genera, Atlanta 

 and Oxygyrus. The shells are small, compressed, and spirally coiled, of a glassy 

 texture, and capable of containing the animal. The gills are situated in a dorsal 

 cavity of the mantle, and the foot is trilobed, one portion of it supporting a minute, 

 subtrigonal operculum. About twenty species are recognizable, Oxygyrus being 

 represented by only two. They abound in the warmer parts of the Atlantic, Indian, 

 land Pacific Oceans. 



Atlanta peroni (magnified). 



