doubted; but we should compare their numbers not merely with those that now exist upon the earth, but with a far larger amount*. We have no reason for believing that the number of species on the earth at any former period was much less than at present; at all events the aquatic portion, with which geologists have most acquaintance, was probably often as great or greater. Now we know that there have been many complete changes of species; new sets of organisms have many times been introduced in place of old ones which have become extinct, so that the total amount which have existed on the earth from the earliest geological period must have borne about the same proportion tothose now living, as the whole human race who have lived and died upon the earth, to the population at the present time. Again, at each epoch, the whole earth was no doubt, as now, more or less the theatre of life, and as the successive generations of each species died, their exuviæ and preservable parts would be deposited over every portion of the then existing seas and oceans, which we have reason for supposing to have been more, rather than less, extensive than at present. In order then to understand our possible knowledge of the early world and its inhabitants, we must compare, not the area of the whole field of our geological researches with the earth's surface, but the area of the examined portion of each formation separately with the whole earth. For example, during the Silurian period all the earth was Silurian, and animals were living and dying, and depositing their remains more or less over the whole area of the globe, and they were probably (the species at least), nearly as varied in different latitudes and longitudes as at present. What proportion do the Silurian districts bear to the whole surface of the globe, land and sea (for far more extensive Silurian districts probably exist beneath the ocean than above it), and what portion of the known Silurian districts has been actually examined for fossils? Would the area of rock actually laid open to the eye be the thousandth or the ten-thousandth part of the earth's surface? Ask the same question with regard to the Oolite or the Chalk, or even to particular beds of these when they differ considerably in their fossils, and you may then get some notion of how small a portion of the whole we know. But yet more important is the probability, nay, almost the certainty, that whole formations containing the records of vast geological periods are entirely buried beneath the ocean, and for ever beyond our reach. Most of the gaps in the geological series may thus be filled up, and vast numbers of unknown and unimaginable animals, which might help to elucidate the affinities of the numerous isolated groups which are a perpetual puzzle to [* See on this subject a paper by Professor Agassiz in the ‘Annals' for November 1854.-ED.] the zoologist, may there be buried, till future revolutions may raise them in their turn above the waters, to afford materials for the study of whatever race of intelligent beings may then have succeeded us. These considerations must lead us to the conclusion, that our knowledge of the whole series of the former inhabitants of the earth is necessarily most imperfect and fragmentary, as much so as our knowledge of the present organic world would be, were we forced to make our collections and observations only in spots equally limited in area and in number with those actually laid open for the collection of fossils. Now, the hypothesis of Professor Forbes is essentially one that assumes to a great extent the completeness of our knowledge of the whole series of organic beings which have existed on the earth. This appears to be a fatal objection to it, independently of all other considerations. It may be said that the same objections exist against every theory on such a subject, but this is not necessarily the case. The hypothesis put forward in this paper depends in no degree upon the completeness of our knowledge of the former condition of the organic world, but takes what facts we have as fragments of a vast whole, and deduces from them something of the nature and proportions of that whole which we can never know in detail. It is founded upon isolated groups of facts, recognizes their isolation, and endeavours to deduce from them the nature of the intervening portions. Another important series of facts, quite in accordance with, and even necessary deductions from, the law now developed, are those of rudimentary organs. That these really do exist, and in most cases have no special function in the animal economy, is admitted by the first authorities in comparative anatomy. The minute limbs hidden beneath the skin in many of the snake-like lizards, the anal hooks of the boa constrictor, the complete series of jointed finger-bones in the paddle of the Manatus and whale, are a few of the most familiar instances. In botany a similar class of facts has been long recognized. Abortive stamens, rudimentary floral envelopes and undeveloped carpels, are of the most frequent occurrence. To every thoughtful naturalist the question must arise, What are these for? What have they to do with the great laws of creation? Do they not teach us something of the system of Nature? If each species has been created independently, and without any necessary relations with pre-existing species, what do these rudiments, these apparent imperfections mean? There must be a cause for them; they must be the necessary results of some great natural law. Now, if, as it has been endeavoured to be shown, the great law which has regulated the peopling of the earth with animal and vegetable life is, that every change shall be gradual; that no new creature shall be formed widely differing from anything before existing; that in this, as in everything else in Nature, there shall be gradation and harmony,-then these rudimentary organs are necessary, and are an essential part of the system of Nature. Ere the higher Vertebrata were formed, for instance, many steps were required, and many organs had to undergo modifications from the rudimental condition in which only they had as yet existed. We still see remaining an antitypal sketch of a wing adapted for flight in the scaly flapper of the penguin, and limbs first concealed beneath the skin, and then weakly protruding from it, were the necessary gradations before others should be formed fully adapted for locomotion. Many more of these modifications should we behold, and more complete series of them, had we a view of all the forms which have ceased to live. The great gaps that exist between fishes, reptiles, birds and mammals would then, no doubt, be softened down by intermediate groups, and the whole organic world would be seen to be an unbroken and harmonious system. It has now been shown, though most briefly and imperfectly, how the law that "Every species has come into existence coincident both in time and space with a pre-existing closely allied species," connects together and renders intelligible a vast number of independent and hitherto unexplained facts. The natural system of arrangement of organic beings, their geographical distribution, their geological sequence, the phænomena of representative and substituted groups in all their modifications, and the most singular peculiarities of anatomical structure, are all explained and illustrated by it, in perfect accordance with the vast mass of facts which the researches of modern naturalists have brought together, and, it is believed, not materially opposed to any of them. It also claims a superiority over previous hypotheses, on the ground that it not merely explains, but necessitates what exists. Granted the law, and many of the most important facts in Nature could not have been otherwise, but are almost as necessary deductions from it, as are the elliptic orbits of the planets from the law of gravitation. Sarawak, Borneo, Feb. 1855. XIX.-On some new Species of Hemipedina from the Oolites. By THOMAS WRIGHT, M.D., F.R.S.E. SINCE the publication of our paper in the August Number of the Annals and Magazine of Natural History,' on the new genus Hemipedina and the Synopsis of the species included therein, our friend S. P. Woodward, Esq., has kindly sent us three new English forms of this group, one found in the calcareous grit of Berkshire, and two in the Kimmeridge clay of Bucks; our friend Thomas Davidson, Esq., has likewise communicated a figure of one found by M. Bouchard Chantereaux some years ago in the Kimmeridge clay of Boulogne-sur-Mer ; we lose no time therefore in recording these additions to the Oolitic fauna, at the same time returning our hearty thanks to the kind friends who have so liberally communicated the specimens. A. Species from the Calcareous Grit. Hemipedina Marchamensis, Wright, nov. sp. Test large, and depressed; ambulacral areas narrow, with two rows of marginal tubercles, nearly as large as those of the interambulacra, extending regularly and without interruption from the peristome to the apical disc, and separated by a zigzag line of small granules down the centre, the areas retaining a nearly uniform width throughout; poriferous zones form a slightly waved line, from every three pairs of pores being set slightly oblique to the line of the zones; interambulacral areas four times the width of the ambulacral, with eight rows of tubercles at the equator, each tubercular plate supporting four nearly equal-sized tubercles abreast; bosses prominent; areolas surrounded with incomplete circlets of small granules; mouth-opening less than one-third the diameter of the test; peristome unequally decagonal; five jaws, in situ, each jaw having two broad flat central ridges, and two oblique marginal ridges with two intervening depressions; teeth long, and obliquely truncated at the points. Dimensions. Transverse diameter 2 inches; height 1 inch? Locality. The calcareous grit of Marcham, Berks. B. Species from the Kimmeridge Clay. Hemipedina Morrisii, Wright, nov. sp. Form and size unknown; test small; ambulacral areas with two rows of regular prominent marginal tubercles gradually diminishing in size from the base to the apex of the areas, and separated by a zigzag line of small granules down the centre; poriferous zones slightly waved; pores large, the pairs separated by thin septa; interambulacral areas more than three times the width of the ambulacral, with six rows of tubercles at the equator, each plate supporting three nearly equal-sized tubercles abreast; bosses prominent; areolas surrounded by incomplete circlets of small granules. Spines referred to this species long, round, slender, and sculptured with delicate longitudinal lines; articulating cavity small, with a smooth rim; head thick, with a thin prominent finely milled ring; body long, much more slender than the head. Locality.-Kimmeridge clay, Hartwell, Bucks. Coll. Professor Morris. Hemipedina Cunningtonii, Wright, nov. sp. Form unknown, upwards of an inch in diameter; ambulacral areas with two marginal rows of very small tubercles rather irregular in their mode of arrangement; poriferous zones nearly straight; interambulacral areas three times the width of the ambulacral, with two rows of tubercles situated on the zonal half of the tubercular plates, leaving thereby a wide intertubercular space which is filled with 8 to 10 rows of small granules; the bosses large and prominent, and the tubercles of a proportionate size; areolas surrounded by a complete circlet of small granules the same size as those filling the middle of the areas. Locality.-Kimmeridge clay near Aylesbury. Collected by Professor Morris. Coll. British Museum, Foreign Species from the Kimmeridge Clay. Hemipedina Bouchardii, Wright, nov. sp. Test large, depressed; ambulacral areas with two rows of regular marginal tubercles extending without interruption from the peristome to the apical disc, and separated by a median zigzag line of small granules; poriferous zones straight; interambulacral areas three times the width of the ambulacral, with ten rows of tubercles at the equator, each tubercular plate having five tubercles abreast; areolas surrounded by circlets of small granules; spines slender, sculptured with longitudinal lines. Dimensions.-Transverse diameter 24 inches? Locality.-Kimmeridge clay, Boulogne-sur-Mer. Collected by M. Bouchard Chantereaux. Coll. M. Bouchard Chantereaux at Boulogne. In the present state of our knowledge it would be premature |