I A N T H I N A 



Genus lANTHINA, Lamarck. 

 Testa subylobosa, nunc depressa nunc conoidea, rarissime 

 umiUicata, tenuis, subpellucida, plus minus violaceo 

 tincia, anfraclibus iiiterdum lavibns, interdum laniel- 

 lato-rugosis, ruyis ad peripheriam sinuanlibus, eolu- 

 melld tenui, prolongatd, aperlurd subampld, labro 

 simplici, medio plerumque sinuato vel etnarginalo. 

 Shell subglobose, sometimes depressed, sometimes conoid, 

 veiy rarely umbilicated, thin, subtransparent, more 

 or less stained with violet, whorls sometimes smooth, 

 sometimes lamellately wrinkled, the wrinkles sinua- 

 ting at the periphery, columella thin, prolonged, aper- 

 ture rather large, lip simple, generally sinuated or 

 notched in the middle. 

 The beautiful oceanic shells comprised in this mono- 

 graph are not uncommon, but they have never been spe- 

 cially investigated, and their varieties of form have never 

 been fairly submitted to the test of comparison. To argue 

 that the shells of lanthina are all modifications of one and 

 the same species, varying according to sex or geographical 

 position, simply because they are characterized by an un- 

 usual uniformity of convolution and colour, is erroneous. 

 The specific differences of shells are often best defined 

 where there is a marked resemblance of general character, 

 and so it is with lanthina. This mollusc, as is well known, 

 is an inhabitant of the open sea, feeding on the gelatinous 

 Velella and other surface fry, and buoying itself on the 

 waves by means of an agglomeration of air-bladders, be- 

 neath which are secreted the eggs. It results that the 

 lanthinte have a wide range of habitation, and few shore 

 stations are recorded as habitats except where a tempes- 

 tuous sea may have wafted the animal in troops upon the 

 sands at comparatively distant intervals. Instances are 

 known where a period of twenty years and more has 

 elapsed before the locality has been again visited by the 

 same mollusc. In some tropical waters, on the other 

 hand, the lanthina have been observed in such shoals as 

 to be deposited on the shore in a series of violet ripples. 



To relate the history of lanthina we must go back two 

 centuries and a half, to the time of Fabius Colonna, a 

 member of the illustrious house of Colonna, who wrote 

 a special work on the purple-yielding creatures of the 

 ocean, De Purpura, etc., 1616, and to whom the lanthina, 

 both shell and animal, was known. Linnaaus included a 

 species in his genus Heliic. Lamarck observed and de- 



scribed two species, founding the present genus for their 

 reception, and ten more have been described since bis time 

 in different works by De Blainville, Leach, D'Orbigny, 

 Menke, and others. 



Owing to the gregarious habits of the lanthina, their 

 habitats are very imperfectly known. The Atlantic and Pa- 

 cific Oceans lay claim to all that have been actually cap- 

 tured. Three species are recorded by Forbes and Hanley 

 as having been washed upon the British shores, and I have 

 authority for adding a fourth. 



Species 1. (Fig. 1 a and 1 b, Mus. Cuming.) 

 Ianthina koseola. lanth. testa ovato-conicd, spird 

 subelatd, anfractibua convexis, oblique plicato-striatis, 

 spiraliter subobsolete lineari-suleatis ; calcareo-albidd, 

 subopacd, violascente tinctd, subtus vivide violaced, 

 columella et apertures fauce carneo-rosaceis; colunielld 

 prolongatd, teiuw contorta. 

 The koseate Ianthina. Shell ovalely conic, spire 

 somewhat elevated, whorls convex, obliquely plicately 

 striated, spirally rather obsoletely linearly grooved ; 

 chalk-white, rather opaque, faintly tinged with violet, 

 deep-violet beneath, columella and interior of the 

 aperture tinged with flesh-rose ; columella prolonged, 

 thinly twisted. 

 Hab. Island of Nicobar. 



The chief characteristics of this species consist in the 

 semi-opaque chalky texture of the last whorl, which is 

 more convex than in the nearest allied form, /. affinis ; 

 and in the surface being more or less obsoletely spirally 

 linearly grooved or scratched. The roseate colouring of 

 the aperture and columella are also peculiar. The speci- 

 mens in Mr. Cuming's possession were collected at the 

 Island of Nicobar in the voyage of the ' Galatea.' 



Species 2. (Fig. 2 a and 2 b, Mus. Cuming.) 

 Ianthina affinis. lanlh. testa ovato-conicd, spird sub- 

 elatd, anfractibm decliti-convexis, submalleatis, siiper- 

 ficiliater decussatim striatis; violascente-albd, nitidius- 

 culd, subtus intense violaced; columelld tenue recurvd. 

 The allied Ianthina. Shell ovately conic, spire 

 somewhat elevated, whorls slopingly convex, some- 

 what indented, superficially decussately striated; vio- 



December, 185 S. 



