JANTHINA. 



JANTHIXA. 



300 



XeriUeeaa*, between which family and the Macrostornrs it appears iu 

 lua 1*1 of Phytophagous (Plant- Eating) Trachelinoda, 



COVMT assign, to UM Ja*iltim<r a place among his Peotinibranchiate 

 QaetropoHe. between the /Vaiilsf7si and UM fftrita. 



De BUinville elevates UM group into a family, under the name of 

 OxyitoaMS, being the fifth an,llo.'. of hi. order JMpftMrfrwMftMa 

 This fiunily comes next to UM Homicyclostomes, which comprise the 



II. Rang mak /an'* wo a genus of the Trochoidi of Cuvier, giving 

 it a poaition between Ami>ullaria, Lam., and Litwpa, Rang. 



Thu nous bos the following chancU-ra : Animal with a very large 

 head and a proboecidifortn muxxle, at the extremity whereof is tht 

 mouth, furni*bd with two Tcrtical subcartiUginous lipa (which are 

 wined with long and very aharp points curved inwarda), and with a 

 lingual enlargrmmt (rraflement) ; tenUclea two, conical, pointed, 

 not very contractile, and very distant, each bearing at iu base a rather 

 loof peduncle, which is oculatod beneath ita extremity; foot oval, 

 divided into two parts, the anterior being concave and in the form of 

 * cupping glass (ventotue), the Utter flattened, thick, and fleshy ; 

 natatory appendage* lateral, rather large and fringed ; respiratory 

 cavity vrry open, and containing two pectinated bronchia; ; orifice of 

 the ovary at the bottom of this cavity ; exciting male organ very 

 null and on UM right tide. 



Shell vrntricoee, globular, or conoid, very fragile, with a low spire, 

 and the lat whorl larger than all the rest together; aperture large, 

 nbtriangular, with disunited bonier*; the columella straight and 

 long, forming the whole of the left border or lip; right border or lip 

 trenchant, and often notched in the middle ; colour of all the species 

 hitherto discovered violet, more or less intense. 



Operculum modified into a vesicular appendage, which serves to 

 mtptT" 1 the animal at the surface of the water, and which adheres to 

 UM posterior and fleshy part of the foot 



I Oceanic Shell (J<u,tMM/rafili,,. Shell with the aninuil, the 



float expanded. 



m, head ; 6, mouth ; r, tentacle* ; d, ejes ; f, border of the mantle at the 

 eaUuwe of UM branchial cavliy ; /, foot, the posterior part, which it flat ; 

 I, Utml expansion of the nuntlr, provided for swimming ; *, foot, anterior 

 part forming s tort of pouch ; i, bunch of .erated voider-, nerving to suspend 

 UM awllnw ( UM ratface of the water ; , eggs impended under the vesicular 

 toaeb; . shell. (Hng.) 



The geographical distribution of this genus is very extensive, the 

 tana having been met with in the four quarters of the world floating 

 oo the ocean or driven on the shores by tempests. It has occurred on 

 UM coasts of our own islands, but there is reason for thinking that it 

 is not to be found in very cold latitudes. In warm climates it is very 

 plentiful. 



Sir Everard Home published in the 'Philosophical Transactions' 

 for 1817 a paper which is appended (Appendix. No. iii.) to Captain 

 Tuckey's Narrative of the Expedition sent to explore the River Zaire, 

 anally call*.! the Congo,' wherein be describes and figures among 

 other ova of Molluscs, or Vmntt tatacta, as he denominates them, 

 UM cameraUd nidus of 7/r/ir Janthina (pi. xiii., figs. 1, 2, 3, 4, 6, 6). 

 " This animal," observes 8ir Everard, " not living at the bottom of 

 the sea, like UM Kernel trilafra in general, deposits iU ova II|M.II it< 

 own shell, if nothing elae oomes in its way. One of the specimens of 

 UM shell of UM JaxUina caught in tho voysge to the Congo fortu- 

 nately baa the ova so deposited." And ho then refers to the drawings 

 of Mr. Baoer, engraved as above quoted. 



In the 4th voL of tb. Journal of the Philadelphia Academy' will 

 be found Remarks on UM Floating Apparatus and other peculiarities 

 of UM gnus Janthina,' by Reynall Coatos, M.D. This highly inter- 

 sting paper, UM nralt of UM author's personal observations during a 

 voyage to the Eart Indie*, ertablishes tb* correctness of Cuvier's 

 remark, that no anatomical connection exists between the animals and 

 UM olr-o.il. of their float ; but does not corroborate the view, of Sir 

 Everard as to UM onwrated nidus on the shell which he saw with so 

 * tcMon. Ih-. Coatos placed some Janlhinir. in a tumbler of 

 brine, and having ramoved a portion of the float of one with scissor*, 

 the animal soon set to work to .npply the deficiency after the following 

 -TlM foot was advanced upon the remaining vesicle, until 

 boot two-third, of that part rose above the surface of the water; 

 h was then expanded to UM uttermost, and thrown back upon the 

 water, like the foot of a fM*M wbra it begins to swim ; it was then 

 contracted at UM dgrs, and formed into UM shape of a hood, inclosing 



a globule of air, which was slowly applied to the extremity of tlio 

 float. There was now a vibratory movement throughout the foot, 

 and when it was again thrown back to renew the process the globule 

 was found inclosed ill its newly-made envelope. From this it result* 

 that the membrane inclosing the cells is secreted by the foot, and 

 that there is no attachment between the float and the animal other 

 than that arising from the nice adaptation and adjustment of proxi- 

 mate surfaces. Dr. Coates states that the float varies in different 

 species. In Janthina frayilit he describes it as convex, subcarinate 

 above and concave beneath, straight, and composed of large vesicles : 

 ib J. globoia he found the vesicles smaller, and the float flat both 

 above and beneath, added to which it is formed by the reunion of one 

 of the edges into a spiral and nearly circular disc. In J. cxigua it 

 was straight, narrow, and flattened, and the vesicles were small. 

 Along the under surface of the float a little line of pearly fibres was 

 remarked, to which are attached the eggs of the animal. 



Although Dr. Coatos had no opportunity of observing the eggs of 

 J. frnyilu, he is strongly inclined to believe that the eggs figured 

 and described in ' 1'hiL Trans.,' as above alluded to, belong to some 

 other marine animal ; and he grounds his belief on the dissimilarity 

 between those figures and tho eggs of J. globota and J. ucigua. In 

 these two species the eggs are contained iu little membranous bags of 

 some consistence, which are attached iii rows to the pearly fibres of 

 the under surface of the float by small filamentous pedicles similar 

 in appearance to the fibres. These bags are covered with minute 

 gelatinous conical eminences, and are partially divided by incomplete 

 septa, as may be seen by the aid of a powerful lens. In J. r 

 the division is very partial ; but in J. globout it gives to the whole 

 sac a chambered appearance. It would seem that the animal con- 

 sumed considerable time in depositing its eggs, for the bags nearest 

 to the extremity of the float were constantly found empty, while tho 

 central bags contained young shells fully formed : those towards the 

 animal were filled with eggs. The probability is, that the young 

 animals when hatched ascend the float of the mother, and thus 

 gaining access to the surface, construct the elements of their future 

 support. 



II. Rang, who also notices Sir Everard's statement, mentions it as 

 certain that Janthina deposits its eggs sometimes iu considerable 

 number, as he has had occasion to remark, under the float, where 

 they are attached by means of small pedicles ; and he goes on to say, 

 that the animal abandons them, together with the float, which in 

 then charged with their preservation. M. Rang adds, that it is 

 possible that, at this epoch, the natatory appendages of the mantle, 

 being sufficiently developed, permit the animal to use them for 

 swimming, and thus supply the loss ; or one must suppose that these 

 animals have the faculty of replacing the float That they have that 

 faculty we have above seen. 



Browne, in his ' Natural History of Jamaica,' gives by no means 

 a bad account of the floats of these animals, many of which he 

 encountered between tho Bermudas and the Western Islands, in his 

 voyage from Jamaica. He says, "I have observed many of the 

 vesicular themselves swimming upon the surface of the water, which 

 induced me to think that they were thrown off as the creatures 

 retired." Sloane also saw these oceanic snails, and figures them. 



In January, 1833, Dr. Grant exhibited to a meeting of the Zoological 

 Society of London numerous specimens of J. vulgarii, Lam., and of 

 Vcleila limbota, Lam., both animals of rare occurrence on the English 

 coast, and chiefly met with floating iu tropical or warmer seas. They 

 were obtained by him at tho beginning of September, 1832, in 

 Whitoond Bay, close to the point of the Land's End, Cornwall, where 

 they were thrown in great numbers on the sands, after a storm of 

 throe days' continuance from tho north-west : they must, he observed, 

 consequently have been floating before they were directed to the 

 coast by the storm, in latitudes at least as high as Unit in which they 

 were found. Dr. Grant regards it as probable that neither of these 

 animals is capable of discharging at will the gaseous fluid by which 

 they are supported on the surface of the sea; otherwise, iu such a 

 violent and continued tempest as that which stranded them, they 

 would have i<mptn.l tln-ir vesicles and have sunk to the stiller 

 bottom. ('Zool. 1'roc,') Browne on the other hand says, speaking 

 of the float, "This raises and sustains it while it pleases to continue 

 on the surface ; but when it wauls to return, it throws off its bladder 

 and sinks." 



Lamarck places Janthina among tho Plant-Eaters : but in the 

 communication by Dr. Grant above noticed, it is suggested that 

 Janthina, a predooeous Gastropod accompanying Velclla, as there 

 described, may prey upon it, and acquire from it the blue colouring 

 matter of its shell. 



Several authors speak of the beautiful purple liquor which the 

 living animal diffuses when it is touched. 



J. frayilit, Common Oceanic Snail, has the shell pale ; body whorl 

 aiigulatt-d ; the base flattened, striated, and deep violet ; aperture 

 broader than long ; outer lip deeply emorginato. (Swainson.) 



It occurs iu warm and temperate climates; several instances are 

 recorded of iU capture on and near the British Islands. 



J. cxigua has been found on the English and Irish coasts. 



J. paUida is a species nearly allied to J. yloboia. This species is 

 very rare, and has been obtained only twice from the coast of Ireland. 



