1

ticulate raised line; the anterior margin more decidedly denticulate than in the Gresford plant; and the style half the length of the carpel, and variable in direction. In specimens gathered by myself in 1832, near Cambridge (see fig. 19), the stigma is peltate, concave, papillose, and irregularly toothed; the anthers four-celled; the fruit and carpels, which are not mature, equally sessile as in the foregoing ; the margins denticulate, and the style similar in relative length. I also possess specimens from Dover (see fig. 20), in which the stigma (a) is peitate, concave, papillose, and irregularly toothed; the fruit (b) rearly sessile; the carpels on rather longer, but still very short, pedicles; the dorsal margin with three denticulate borders, the central one most prominent, and the others somewhat interrupted; the anterior margin distinctly denticulate; and the style half the length of the carpel, and variable in direction. The anthers in the latter specimen I was unable to detect. In all these specimens the style is enlarged at the base, and bears a projecting line, which is continued along the middle of the face of the carpel.

The above results appear to militate strangely against the observation of M. Steinheil, that the entire stigma is accompanied by fourcelled anthers, and the toothed one with two-celled anthers; since in all our specimens, whatever are the number of the cells, the stigma is toothed. They all, likewise, coincide in the relative length of the style to the carpel, in the carpels being almost sessile, and their margins nearly similar in denticulation. Now, as it is admitted by Steinheil that the anther-cells are variable, in one instance at least, in the form with four cells, by the suppression of two of them, why may not the contrary be admitted, that the two-celled anthers are also liable to vary by an increase of one or more additional cells? And from the above this seems plausible; and as all our specimens agree in two other characters of Steinheil's dentata, viz. the toothed stigma and the style half the length of the carpel, we necessarily feel disposed to consider them all as forms of his Z. dentata, notwithstanding the variation in the number of the anther-cells. Without arrogantly presuming to decide confidently on a point in which the most skilful botanists are at issue, it may be suggested that those who possess the facility of examining living specimens, by which alone can the question be decided, would hasten to ascertain whether the only characters which confessedly appear at all constant, are in reality sufficiently so to constitute two good and distinct species, viz. the toothed stigma, and the style half the length of the carpel, in dentata, and the entire stigma, and the style nearly equal to the carpel, in palustris.

VOL. IX., NO. XXVI.

35

274

OBSERVATIONS ON THE ANIMALS INHABITING MULTILOCULAR SHELLS,

CHIEFLY WITH A VIEW TO THE GEOLOGICAL IMPORTANCE OF THE SUBJECT.

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By D. T. ANSTED, ESQ. B.A. F.G.S. F.C.P.S.

OF JESUS COLLEGE, CAMBRIDGE.*

IN a former paper on this subject, which ended rather abruptly, in consequence of a page of MS. having been mislaid, I was proceeding, after certain general remarks, and some account of the family Nautilacea and two genera of Ammoneata, to describe the sub-genera of the important and widely-extended Ammonites; and may be remembered that the first of these, the Goniatites, was the only one of which any extended account was given. Next in order,the Ceratites of de Haan were mentioned as occurring in the muschelkalk beds of the continent; and these differ chiefly from the Goniatites in the nature of the intersection of the chamber with the shell, which in the latter group is angular, whilst in the former it consists of a series of nearly regular curves, alternately semicircles and mere wavy lines. But there is a further difference, causing a nearer approximation to the true Ammonites, in this group; for, instead of the shells being very round and smooth, as the Goniatites almost invariably are, they begin to be provided with tubercles, acting as a sort of compensation for a flattening of the spiral, which generally occurs when these are introduced: for this flattened form, not being so strong with the same thickness of shell as the more rounded shape and more perfect arch of the other group, the tubercles or bosses are introduced, "superadding the strength of a dome to that of the simple arch at each point where these bosses are inserted."

Passing on now to the other Ammonites, we find the line of intersection already spoken of waved in a more and more complicated manner, till it resembles rather the edge of a parsley leaf, or the sutures of a skull, than any thing else one can compare it to, and at the same time the number of bosses or tubercles is increased, and additional contrivances for strength are introduced, the shell often becoming extremely fragile and the siphuncle very minute. In the chalk Ammonites especially the shell is very thin; and it is often a

Continued from page 50 of the last number.

matter of some difficulty, even in large specimens, to discover whereabouts the aperture for the siphuncle is situated.

Now, with regard to the use of this extreme complication of the edge of the chamber, although it certainly seems to add much strength to the whole, there is a secondary object mentioned by M. von Buch, which we must not neglect to notice. He considers that the alternate projections and recesses thus formed must have given firmer hold to the mantle of the animal, and enabled it to retain, in safe and close connexion, the animal and its shell, notwithstanding the small size and inconvenient position of the siphuncle, which, in all probability, is of much use for this purpose in the Nautilacea. Following out the idea, he has traced a remarkable uniformity in the number and positions of the undulations throughout the whole genus of Ammonites. "I think," he says, "it may be considered a question definitively settled that in all species, whatever may be the apparent anomalies of form, it is easy to make out six principal lobes,* with other accessory lobes interposed, which all adjust themselves with wonderful regularity in the circumference of the shell." Between every pair of depressions or lobes there is a raised rounded part, the saddle; and these saddles always correspond in number and position to the lobes.

The system of lobes and saddles, so constant and disposed with such exact symmetry, appeared to M. von Buch to indicate an organization separating very decisively the two families Nautilacea and Ammoneata; and although, perhaps, the conclusions drawn from this view of the subject, and the sub-divisions proposed, are premature, and the facts already determined not quite so important as they have been assumed to be, still much good has been done by the mere convenient classification of so large a genus into distinct groups, which, indeed, our author goes so far as to call " bution claire, positive et utile, en familles naturelles."

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We have one more remark to make on the Ammonites generally, before proceeding to the consideration of the allied genera. Their shells, it would seem, are usually thin, and the siphuncle small; but the former receive great additional strength by the number of ribs, as well as tubercles, not immediately connected with the septa, and fluting, as it were, the part most exposed to pressure; while the

* By the word “lobe” is designated the depressions which occur in the wall of the chamber of Ammonites, &c. caused by the successive bends of the undulations towards the aperture. The raised parts between these hollows are called saddles.

latter the siphuncle-is often undefended, being almost always placed at the extreme dorsal edge of the shell, and sometimes actually outside it.

Lastly, with regard to the distribution of the remaining groups of this genus, it is important to observe that the period throughout the formation of the oolites was by far the most abundant, in every way, in species, as well as individuals. Even in the limited state of our knowledge of the animal kingdom at that time, we can speak to not less than a hundred and fifty distinct species, every one created, living its appointed time, and becoming extinct, between the commencement and close of that series of limestone deposits.

In all parts of the continent of Europe, as well as in Great Britain, the fossils of this genus are extraordinarily abundant; but they are not confined to Europe. Specimens have been found very high up on the Himalaya mountains, in Asia. They occur in the state of New Jersey, and in several other places in North America; in Brazil, and on the coast of Chili in South America: and probably, when future researches shall have laid open the scientific stores of Africa and Australia, other species will there be found, showing the genus to have been once as widely distributed as it was undoubtedly locally abundant.

It is rather singular that out of a number of allied genera, forming together an important natural family, one genus should be among the most widely spread of any that is known, and all the others comparatively very rare, and occupying no important place in the scale of nature. Yet so it is in the case before us; for the Ammonites are not more remarkable for their singular variety and great numbers, than the several genera, closely allied in every thing but external form, are for the very narrow limits within which they are confined. The Hamites, next in order to the Ammonites, are not, indeed, quite so rare as the Scaphites or Turrilites already described; but still they are only met with in a few strata, and in but one of those are they at all abundant. Of the different species known, two occur in the continental beds of the oolites; one so low down as the lias, while there are nearly thirty in the cretaceous group, most of them occurring in the two beds of green sand.

Of the Baculites, which come next, five species only are named at present, and all appear to have lived during the deposition of the chalk. The difference between these two last genera consists, to all appearance, in a very unimportant change of form, the Hamite being, as we have already observed, bent round more or less at the smaller extremity or apex of the long, narrow, and often elliptical

cone, which is the simple and ordinary form of the Baculite. Both are sometimes ribbed, though the latter rarely; and in both the edges of the septa are very complicated. The shells of both, too, are commonly rather thin, the siphuncle not large, and the complete fossil, especially of the Baculite, extremely rare.

So much for the external form of the shells referred to the great natural family Ammoneata; a family which deserves well the consideration of the paleontologist, since of all others it is, as we have already remarked, the most widely spread, the most characteristic of several formations, and which is, moreover, just so nearly allied to living types as to excite our curiosity, and raise our hopes that something may sooner or later appear, some new discovery or closer observation made, by which our speculations may be tested, and their truth or falsity proved.

With a full knowledge, then, of the danger of too rash generalizations, and wishing it to be clearly understood that our theories and attempted analogies are rather thrown out with a view to excite inquiry than with any expectation of satisfying doubts, or still more of deciding dogmatically on any disputed point, we will proceed to the consideration of the following queries, viz. how far the analogies traceable in the shells of the Nautilacea and Ammoneata are indicative of analogous habits, and to what change of habits of the animal the alteration of structure in the two families may most probably refer.

Now, that the subject may be more perfectly understood, let us here just repeat, in as few words as possible, the most important both of the analogies and differences, because, when they are thus put in apposition, our plan of considering the matter will be more clear to the reader, and its value, however small, more truly appreciated.

The shells, then, of the two families, are, in all cases, multilocular, the chambers being filled with air during the life of the animal, and forming then a mass not very different in weight from the weight of an equal mass of water. In other words, the shell would float of

itself under the ordinary conditions. Besides this, the walls of separation of the chambers are always pierced with a hole larger or smaller, through which a tube has passed, communicating with the interior of the animal. There is, in all the species, considerable regard paid to the general strength of the shell in some way or other, more especially where the animal is no longer present, for the empty cells are stronger than the outer one, which is, in most the only one inhabited.