the foot withdraws, quite gently, under water, to remain there if its operations cease, or to move forward again and recommence if its work is to be continued.

When we have counted the number of vesicles at the extremity of the float, and thoroughly observed their arrangement before the manœuvres just indicated, we see, when they have ceased, that another cell has been glued on in front of those which we had ascertained to be the furthest towards the mouth. This first fact proves incontestably that the growth of the float takes place longitudinally and at its anterior extremity. It proves also that it is the foot which manoeuvres in such a manner as to add the new vesicles towards this extremity; and the process of growth is, no doubt, as follows:-The foot, first of all curled up into a cup, had, when applied to the float, a certain thickness of air between it and the latter; by secreting a layer of mucus and then spreading out, it must necessarily join this viscous layer to the rest of the float, and thus keep the air-bubble imprisoned.

We may form an idea of what takes place when we observe a garden-snail or slug creeping upon a body covered with dust: we often find, beneath the train of mucus left behind it by the animal, a bubble of air which is imprisoned between the unmoistened surface of the body and the lamella secreted by the foot. Here we have something produced, mechanically speaking, perfectly similar; but in the former case it is accomplished by design and for a particular purpose.

The mucosity is evidently insoluble in water; and as it dries in the emergent portion, it acquires a certain consistence, which has led to the supposition that it was cartilaginous.

If we admit the process of the formation of the float to be as just described (and it seems difficult to me not to regard it as true, since at each new movement of the foot we count a fresh bubble added), we may easily explain the dissidences of authors, their opinions, and most of the facts which they relate. Thus we understand why the animal, when once at the bottom of the water, is incapable of forming a new float. Most probably the Ianthine which have lost their float are fated to die, unless they be carried to the surface by some cause which I shall not attempt to imagine.

*

To verify the notion which has just been put forward, it was necessary that experiments, varied in several ways, should furnish its confirmation.

Having taken an Ianthina upon a small iron hook and suspended it, not out of the water, but at about that depth below the surface which it occupies when it swims freely suspended

from its float, I remarked that when the first movements preceding its being placed in this position ceased, and the animal believed itself out of danger, it issued by degrees from its shell, extended its foot, and commenced the manoeuvres described above. I had the satisfaction of seeing the opinion that I had formed confirmed in every point, by observing the animals in these normal conditions; for I was able to be present, with the help of patience, at the origin and formation of a float. I saw that, in proportion as one bubble was added to another, the animal became specifically lighter, and was less immersed in the water. And I ascertained that, under these circumstances, the Ianthina which could not reach the surface made vain efforts and movements to form bubbles; and when, under these circumstances, I very gently raised the shell by means of a small hook, as soon as the foot issued from the water, air was imprisoned, a bubble added to the float, and the animal began to reascend. Now, nothing of this could have taken place without the assistance which I gave it.

I have had many individuals of which the floats, being partially destroyed by storms, were insufficient to bring the body of the Tanthina near enough to the surface, and allowed the animals to perish floating at mid water, exactly like those which fell to the bottom of the vessels when completely deprived of aëriferous vesicles.

Dr. Coates, cited by Forbes and Hanley, and already mentioned, supposes that the young Ianthine, on issuing from the capsules suspended beneath the float, in which they passed their first embryonic period, get upon the back of the float, and then attempt the formation of the apparatus which subsequently enables them to do without their mother. This supposition, from what we have just scen, appears to be perfectly legitimate as a supposition. Nevertheless, as this matter is not proved by direct observation, we must not forget that the Gasteropods in an embryonic state have locomotive organs, which enable them to move about, and to come even to the surface of the water; for they are very active. It may be, therefore, that at the moment when the organs of locomotion bring the young Ianthine to the surface of the water, they begin to form with their foot a few bubbles containing air which serve as their first floats.

As all authors have stated, the floats of the Ianthina are delicate; they must be affected by the attacks of the numerous and voracious inhabitants of the sea, and consequently they must also be constantly repaired. It is plain, indeed, that constant secretion would either be too late for the necessities of the economy of the animal, or in advance of it, producing a too great and inconvenient flotation. Hence the restoration of

the float must be entirely subject to the will of the animal, to its appreciation, if I may so speak; and this is really the case, as it never makes use of the mucosity of its foot except when it feels its float to be insufficient, just as the spider employs the silk with which its spinnerets furnish it only when injuries have rendered its web unfit to capture the prey which is necessary for its existence.

It is unnecessary to say that a gaseous secretion is inadmissible, and that there is nothing to warrant its existence.

From all that precedes, I may justly be asked whether I have seen in my aquaria Ianthine entirely deprived of their floats reconstruct new ones. I reply that the animals did not live long enough for this; it is with them as with the spider to which I have just referred: if we destroy its web, it reconstructs this, but at the expense of its body; and if we continue without allowing it to capture a prey, if its organization does not provide itself with what is necessary to repair the losses caused by secreting silk, it is seen to die of inanition. In the same way here the Ianthine are animals of the high sea; they find in these regions their proper food, which they did not meet with, in all probability, in my aquaria; hence they only lived a short. time, exhausted by their exertions and by the want of nourish

ment.

In conclusion, I will remark that Cuvier's opinion, so full of reserve and doubt, cannot be maintained. The float of the Ianthina cannot in any way represent an operculum, or even its distant analogue.

XXXI.-Descriptions of some new Species of Diurnal Lepidoptera in the Collection of the British Museum. By ARTHUR G. BUTLER, F.Z.S., Assistant, Zoological Department, British Museum.

Limenitis Calidasa, n. sp.

L. Calidasa, Moore, MS.

Ala supra fusca, fascia media irregulari albo-viridescente, anticarum maculas octo inæquales formante, posticarum integra, in medio latiore; area basali fascia media interrupta rubra nigro circumdata, basi fascia simili obscura; area apicali fascia submarginali rubra, maculis nigris utrinque marginata; margine postico pallido, lunulis nigris marginato.

Corpus fuscum; antennæ nigræ, rubro acuminatæ.

Ala antica subtus area basali viridi, fascia media rubra a vena media partita, lineaque basali obliqua nigra; area apicali cinerea, venis apud costam rubris, linea rubra undata, maculisque nigris submarginata; fascia media velut supra nigroque utrinque marginata;

margine postico albo, linea fusca marginato, angulis alternis; ciliis albis venis nigro acuminatis.

Alæ postice area basali viridi, lineis sub vena costali duabus, puncto inter nervulos subcostales lineisque quatuor intra cellam nigris; fascia media latiore, lunulis brevibus nigris marginata; area apicali cinerea, fascia rubra velut supra; margine postico albo, lineis duabus fuscis marginato, angulis alternis, venis nigro

acuminatis.

Corpus viride; antennæ ferrugineæ.

Alar. exp. unc. 23.

Hab. Ceylon.

This species is allied to Limenitis Zulema, Doubl. & Hewits. (North India).

Euodia Joanna, n. sp.

Ale anticæ supra fuscæ; macula parva apicali nigra purpureo pupillata, maculaque apud angulum analem majore simili; fasciis duabus fulvis de costa currentibus, una cellam terminante, similique apud apicem; fascia conspersa fulvo inter cellam angulumque analem currente.

Alæ postica fusca, ocello parvo apicali nigro ferrugineo circumdato, maculaque apud angulum analem majore violaceo pupillata. Ala antica subtus fuscæ, fasciis subcostalibus ad angulum analem productis; ocellis ochreo circumcinctis; margine postico lineis duabus pallidis marginato.

Ala postica velut in Euodia Abeona, Donov. (Australia), Hipparchia? Abeona, Doubl. (List Lep. Brit. Mus.), ocellis autem majoribus. Alar. exp. unc. 276.

Hab. Australia.

Closely allied to E. Abeona, Donov., of which it has been hitherto supposed to be a variety; but I can discover no proofs of the identity of the two insects, and have therefore described it as distinct.

It differs from E. Abeona above in having the distinct orange band of the front wings replaced by two pale-yellow streaky bands, and the anal ocellus of the hind wings much larger.

Below, the orange band of the front wings is replaced by a narrower and indistinct pale-yellow band, and the ocelli are more distinctly encircled by pale brown. In the hind wings the ocelli are proportionably much larger and brighter.

Lasiommata mirifica, n. sp.

Alæ antica supra fuscæ, fascia ochrea obliqua lata irregulari, de costa post medium ad angulum analem currente; macula alba inter venas discoidales apud marginem posticum.

Ala postica fuscæ, ocello magno apud angulum analem nigro albo pupillato ferrugineoque circumcincto.

Alæ subtus fusca, cinereo variæ; anticæ fascia ochrea lata macula

que alba; postica punctis albo pupillatis inter venas post alarum medium dispositis.

This species is most closely allied to Lasiommata Merope, Boisduval (Australia). Our specimen is unfortunately in very

bad condition.

We have a female specimen of an insect somewhat more closely allied to this species: it differs from the usual form of L. Merope in having the apical half of the front wings black, the anal spot being small and quite distinct from the basal ferruginous portion of the wing; and the yellow spot below the front-wing ocellus is also replaced by a white spot.

XXXII. Some Account of a new Species of Fern (Polystichum Maderense) recently discovered in the Island of Madeira. By JAMES YATE JOHNSON, Cor. M.Z.S.

I AM indebted to Mr. Joad, a zealous collector and student of Ferns, who has lately spent a few months in this island, for being permitted to examine and describe a Fern, of which he found a single specimen in the Ribeiro de Janella. The two or three fronds submitted to me show that the Fern is exactly intermediate between Polystichum falcinellum, Presl, and P. angulare, Presl, both of them natives of this island, the former being, as far as is known, peculiar to Madeira. Widely as these two forms appeared to be separated, they are certainly brought into close contact by the Fern which I now shortly describe.

The facies of the frond at once suggests an alliance with P. angulare. It is lanceolate, lax, and subbipinnate; that is, the pinnæ are divided nearly to the midrib, and the lobes are narrowed, but not stalked, below. Each lobe has at its tip a short but conspicuous aculeus. The first lobe on the upper side of each pinna is elongate; and here we have an approach to P. falcinellum, a resemblance which is further displayed in the form of the pinnæ at the upper end of the frond, and in the structure of the scales on the rachis, which are long and somewhat hair-like. The arrangement of the sori are more like what is seen in P. falcinellum than in P. angulare. The indusia are those of the genus.

The fronds of the specimen are upwards of 24 inches in length. Further researches may show that this is only a variety of P. falcinellum; but for the present it seems best to register it as a distinct species.

Madeira, March 3, 1866.