14 MOLLUSCA. HETEROPODA. 



ORDER I. HETEROPODA. 



Body free, elongated, swimming horizontally ; head distinct ; 

 two eyes ; no arms arranged round the head ; no foot under 

 the belly or throat for creeping ; one or more fins, without 

 regular order, and not arranged in pairs. 



The Heteropodes, according to Lamarck, may be considered as part of a series of 

 animals intermediate between the Cephalopoda or Fishes. Between these animals 

 and the fishes, however, there exists a wide hiatus, which it is probable may yet be 

 filled up by the observation of animals hitherto concealed in the depths of the ocean. 



Gen. 1. PHYLLIROE, Lamarck. 



Body oblong, much compressed, nearly lamelliform ; a single 

 fin formed by the tail ; branchiae internal and resembling 

 granulated threads ; head distinct ; two tentacula ; two eyes ; 

 and a retractile proboscis. 



P. bucephalum, Peron. Gelatinous, extremely compressed, so trans- 

 parent that when swimming the head and branchiae alone are 

 perceptible. Inhabits the Mediterranean sea Lam. vii. 678. 



Gen. 2. PTEROTRACHEA, Lam. 



Body free, elongated, gelatinous, pellucid, terminated posteriorly 

 by a tail, and furnished with one or more fins ; branchiae pen- 

 niform, protruding externally, and placed along with the heart 

 under the belly, near the commencement of the tail ; head 

 distinct ; two eyes ; jaws horny ; no tentacula. 



P. coronata, Lam. Belly and tail penniferous ; head terminated by 

 a cylindrical perpendicular proboscis ; ten spines upon the fore- 

 head. Inhabits the Mediterranean sea Lam. vii. 676. 



P. hyalina, Lam. Head elongated, smooth ; body furnished with a 

 central fin. 1 inch long Lam. vii. 676. 



P. pulmonaia, Lam. Head obtuse, hyaline ; respiratory viscus ci- 

 liated ; a single rounded and longitudinal fin. Lam. vii. 676. 



P. aculeata, Lam, Belly destitute of fins ; the tail longer than the 

 trunk, furnished with five rows of spines and terminated by a 

 horizontal fin. Lam. vii. 677- 



Gen. 3. CARINARIA, Lam. 



Body elongated, gelatinous, pellucid, terminated posteriorly by 

 a tail, and furnished with one or with several unequal fins ; 

 heart and branchiae united into one mass, which projects from 

 the belly, is situated near the tail, and inclosed in a shell ; 

 head distinct, furnished with two tentacula ; two eyes ; a con- 

 tractile elongated mouth. Shell univalve, conical, compressed 

 on the sides, unilocular, very thin, hyaline; the apex rolled up 

 into a spire ; the back sometimes furnished with a dentate 

 keel ; aperture oblong, entire. 



