408 Mr. W. H. Benson on Ianthina, Bolten. 



to prove a more extensive range for the known species of this 

 ubiquitous genus. 



/. exigua, Lamk. 



Sketches were made, in different positions, of the animal taken 

 near Madeira. Bunches of purple ovisacs adhered to the centre 

 of all the floats, those towards the hinder extremity being flaccid 

 and empty. When the float is broken off, the animal sets to 

 work to supply its place in the mode described by Reynell Coates. 

 A free float was captured with ovisacs attached, but without the 

 shell and its inhabitant. The shell, from its small size and its 

 position, is not visible in the water, but the float may be easily 

 distinguished from the foam scattered from the bows of the ship, 

 by its whiter appearance, resembling a minute flock of cotton, 

 broad at one end and pointed at the other. No additional egg- 

 sacs were deposited while the animals remained in confinement, 

 although they continued to add to their floats. There are flexible 

 cilia to the mouth ; when the snout is extruded, these are ex- 

 tended and agitated with great rapidity, apparently in the search 

 for food. 



Confined with Glaucus Forsteri, I. exigua became the prey of 

 the more active Mollusk ; and portions of the Ianthina, hardly 

 changed, were voided from a small papilla situated between the 

 second and third branchiated fins of Glaucus, on the same side 

 as the conspicuous organ of generation. 



The tentacula of 7, exigua are elongate-conical, not subulate 

 as in Rang's figure of I. violacea ?; and the apophyses, which he 

 describes as ocular pedicles, are larger and broader in proportion 

 than in his species, emulating the tentacula in size. Morch 

 places Bang's shell in the subgenus Achates, while /. exigua is 

 included in Iodina. It is highly probable that a critical exami- 

 nation and dissection of the animals will establish generic dif- 

 ferences among the Ianthince. An opportunity occurs on our 

 own shores for comparing those which are brought to the western 

 portions of the British Islands by the Gulf- Stream. 



All the varieties of /. exigua from the Atlantic and the eastern 

 seas presented a more rounded base than the British specimen 

 figured by Reeve, which was probably imperfect in that part. 

 The emargination of the outer lip is very variable in perfect 

 specimens, some of the Madeiran and south-eastern shells exhi- 

 biting an incision nearly as deep as that observable in /. bifida. 

 The Madeiran type has a bluer tint than the more southern 

 forms. There is a greater or less tendency to perforation in all 

 the varieties — a feature which appears to have been overlooked. 

 The apex is more or less developed ; and the paler band round 

 the suture is present in some specimens, and deficient in others, 

 from the same locality. 



