186 IANTHINIDiE. 



widely dissimilar shells. Lamarck defined the genus 

 and made it recognizable. It was at one time placed 

 by the last-named author in his class Heteropoda, a di- 

 vision based on the anomalous character of the foot and 

 pelagic nature of the animal ; but this class was repu- 

 diated by Cuvier, and is not maintainable in a scientific 

 point of view. The organization of Ianthina does not 

 differ in any essential respect from that of other Gas- 

 tropods. Its synonyms are not numerous ; they are 

 chiefly mere MS. names, viz. Neritoidea, Humphreys, 

 Ianthinus, De Montfort, Amethistina, S chintz, lodes, 

 Leach, and Achates, Gistel. The old Dutch naturalist 

 Rumph called it " Quallebootje," translateable as the 

 boat of a Holothuria ; and De Montfort agreed with 

 him in the propriety of the name, believing that lan- 

 tliina had a greater affinity to that animal than to the 

 Mollusca ! 



Ianthina rotunda'ta*, Leach. 



/. rotundata (Leach, MS.), Dillwyn, Contributions towards a History of 

 Swansea (1840), p. 59. /. communis, F. & H. ii. p. 549, pi. lxix. f. 6, 7, 

 & cxxxiii. f. 1. 



Shell forming a depressed cone above and a shorter one 

 below, somewhat globular, with a bluntly angulated periphery, 

 thin, semitransparent, and glossy : sculpture, minute and close- 

 set spiral striae, which are often wavy and interrupted by the 

 flexuous lines of growth ; the base exhibits stronger interme- 

 diate spiral striae : colour white, tinged with purple or mauve 

 on the upper side, deepening into violet beneath ; a broad and 

 deeper-hued band sometimes encircles the base, which is then 

 whitish, like the upper side : the apex or nucleus is pale am- 

 ber-colour: spire abrupt: ivhorls 4' (besides 3 which consti- 

 tute the stiliform apex), swollen and bulging outwards, com- 

 pressed and sloping towards the suture ; the last is three or 

 four times the size of all the rest put together ; the apex or 

 nucleus (which resembles in shape the shell of Stilifer Turtoni) 



* Bounded. 



