species of Amblodon in different parts of the United States and that this type is not limited to the Northern States but extends west as far as the western parts of Missouri and South as far as Louisiana and Alabama.

AMBLODON, Rafin.-External characters of Corvina, combined with the form and appearance of Pogonias. Upper pharyngeals distinct, covered with broad, hemispherical teeth closely set, like pavement stones and arranged in regular rows; outside of these are a few small pointed teeth. The lower right and left pharyngeals are soldered together into a broad triangular plate, covered with teeth of the same kind and arranged in the same manner as upou the upper pharyngeals. In the genus Corvia the lower pharyngeals are distinct as the upper oues and support short conical teeth not numerous, nor closely set. From want of a sufficient number of specimens I am unable to determine whether the specimens from the great Lakes are specifically identical with. those of the Ohio River described by Rafinesque as Amblodon grunniens; but I have ascertained that the species of the Ohio River differs from that of Huntsville, which I call Amblodon concinnus, Agass. This species differs from A. grunniens in having the body less elongated, the profile steeper, and the dorsal fin placed further forwards. The profile is most arched immediately over the upper attachment of the preopercle, in A. grunuiens it is most prominent over the opercule. The dorsal fin ends slightly in advance of the base of the pectorals; in A. grunniens behind these. The serrated edge of the preopercle is directed more obliquely downwards and backwards, making the inferior angle of the preopercle more acute. This species is known in the Tennessee River by the name of Drum. It reaches there the weight of fifty pounds.

Ambledon lineatus, Agass.-This species sent to me by Mr. Geo. Stolley from the Osage River, Mo., resembles more A. concinnus than A. grunniens, but the head is shorter; the prominence of the forehead is nearer the dorsal fin, immediately over the opercle, thus having a less arched profile. The anterior border of the eye nearly reaches the profile of the head. The spines of the dorsal fin are bent more backwards. The dark coloration of the centres of the scales, especially in younger specimens produces the appearance of regular lines following the direction of the rows of scales. hence the name of this species. It grows also very large, and bears in Missouri the same name of Drum as the species of the Tennessee, River. Mr. Stolley informs me that the Amblodons are very sluggish, and live at the bottom of muddy waters, where they are often seen progressing slowly, raising as it were, clouds of dirt before them, now lying upon one side of their body, then turning upon themselves or

plunging headlong into the soft ground with their body in a ver- / tical position. They feed upon worms, and small shells, large numbers of which are often found crushed to pieces in their stomach; they however bite occasionally at a minnow.

Esoces, Cuv. (Joh. Müller.)-Though we have only the genus Esox representing this family in North America, it is perhaps not superfluous for me to state that I agree with the modifications. J. Müller has introduced in this group since it was first established by Cuvier. We have one species from the Tennessee River, called Pike at Huntsville.

Esox crassus, Agass.-This species agrees fully with the type of Esox reticulatus in having both the operculum and cheeks covered with scales. It is, however, a much deeper fish than E. reticulatus; its scales are larger and nearly of an hexagonal form. The scales of the preopercle and cheeks are as large as those of the body; those on the opercle are smaller. The superior orbital ridges are more prominent; the depression between these ridges is deeper. The anal and caudal fins are shorter. The body is marked as in Esox reticulatus. The genus Esox has a very wide range in North America, but there is no difference of structure between those of the Canadian Lakes and the western waters, and those of the Atlantic lakes and rivers, as Mr. Girard affirms in a notice recently published in the Proceedings of the Academy of Natural Sciences in Philadelphia (1853, page 386). In the first place my Esox Boreus, from Lake Superior, does not belong to the same type as Esox Estor, its cheeks being covered with scales. Moreover, I know already three species from the western waters, one of which is noticed above, the cheeks and operculum of which are as completely covered with scales as in Esox reticulatus. There are in reality more species of the type of Esox reticulatus, in the western waters and the Canada lakes, than of the type of Esox Estor, and far from excluding one another these types occur there together. As to the application of the names Pike and Pickerel to the different type of our Esoces, it cannot be justified, since such a use would be a scientific sanction of the misapplication of English names to our native animals, which has already led to so much confusion. Unless applied as a generic apellation, the name Pike must be retained for the European Esox Lucius, to which only it belongs by right; whilst the name Pickerel designates the young of that fish. It would be quite as advisable to introduce in our scientific nomenclature the name of Calf to distinguish the Bisons from the type of our domesticated cattle, as to apply the name Pickerel to any particular species or set of species of the genus Esox.

(To be continued.)

THE

AMERICAN

JOURNAL OF SCIENCE AND ARTS.

[SECOND SERIES.]

ART. XXXII.-The Primitive Diversity and number of Animals in Geological Times; by L. AGASSIZ.

THERE is a view generally entertained by naturalists and geologists that genera and species of animals and plants are greatly more numerous at the present age of the world than in any previous geological period. This seems to me an entire misconception of the character and diversity of the fossils which have been discovered in the different geological formations, and to rest upon estimates which are not made within the same limits, and with the same standard. Whenever a comparison of the diversity and number of fossils of any geological period has been made with those of the living animals and plants belonging to the same classes and families, it has been done under the tacit assumption which seems to me entirely unjustifiable, that the fossils formerly inhabiting our globe are known to the same extent as the animals which live at present upon its surface; while it should be well understood that however accurate our knowledge of fossils may be, it has been restricted, for each geological formation, to a few circumscribed areas. Comparisons of fossils with the living animals ought, therefore, to be limited to geographical districts corresponding in extent to those in which the fossils occur; or, more properly, a fossil fauna with all its local peculiarities ought to be compared with a corresponding fauna of the present period, and not with all the animals of the same class living at present upon the whole surface of the globe. And when this is done SECOND SERIES, Vol. XVII, No. 51.-May, 1854.

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with sufficient care and proper allowance is made for the limited time during which investigations of fossils have been traced compared with that which has been almost everywhere devoted to the closer study of living animals, it will be seen that the number and diversity of species peculiar to each special fossil fauna is, in most instances, equal to those found to characterize zoological provinces of similar boundaries, at the present day. And this may be said of the fossil fauna of all ages. In many instances the result is even quite the reverse of what is generally supposed to be the fact, for there are distinct fossil fauna which have yielded much larger numbers of species, presenting a greater variety of types than any corresponding fauna in the present age. Some examples will justify this perhaps unexpected statement.

The number of species of shells which are found living along the shores of Europe, does not exceed six hundred. About six hundred species is again the number assigned to the whole basin of the Mediterranean, including both the European and African coasts. Now the most superficial comparison between them and the fossil species which occur in the lower tertiary beds in the vicinity of Paris, shows the latter to exceed twice that number; there are indeed twelve hundred species of fossil shells now known from the eocene beds in the immediate vicinity of Paris, affording, at once, a very striking evidence of the greater diversity and greater number of species of that geological period when compared even with those of a wider geographical area at the present day.

If it be objected that the variety of forms which occur in tropical fauna is greater than that which we observe on the shores of our temperate regions, and that the temperature of the tertiary period having been warmer we may expect a larger number of fossil species from those deposits, I would only refer to local enumerations of marine shells from several tropical regions, to sustain my assertion that the number of fossil shells of the eocene beds of the immediate vicinity of Paris, is much greater than that of any local fauna of the present period, even within the tropics. A catalogue of not quite three hundred species of shells given by Dufo as occurring around the Sechelles Islands, the extent of which may fairly be compared with that of the lower tertiary beds around Paris, will suffice to show, that in a tropical local fauna the number of species known to exist in the present day is far inferior to the number of species known to have occurred during the deposition of the lower tertiary beds in the vicinity of Paris. Another catalogue by Sganzin, of the shells found about Mauritius, Bourbon and Madagascar, gives also less than 300 species for that extensive range of seas surrounding those islands. Let us further compare the results of the investigations of the shells of the Red Sea by Hemprich, Ehrenberg and Rüppel, and there

again we find a smaller number, and a more limited variety of types than are found in the tertiary of Paris; for the whole basin of the Red Sea has thus far yielded only 400 species of shells. Let us finally take the most accurate survey of this kind we have of any shore, that of Panama by Prof. Adams, extending over 50° of latitude, 28° N. of the equator, and 22° S. of it, including the most favorable localities for the growth of shells in the Pacific under the tropics, and yet we shall find his list exceeding but little the number of 500 species. In this instance again we find that the advantage in number and variety is in favor of the tertiary period, and not of the present age. If a different result has been obtained by the estimates made before this, it is owing to the circumstance, that the fossils known from a few localities within narrow geographical limits were compared with the living species known to occur upon the whole surface of the globe. But let us trace these comparisons through other geological periods, with reference to other classes also, and we shall find in every instance, similar results. The tertiary fossils of Bordeaux, though less numerous in species than those of the eocene in the vicinity of Paris, will compare with any local fauna of the present period as favorably for variety and number of species as those of the lower tertiaries. This may be said, with the same certainty, of the tertiary shells of the Sub-appennine Hills, or of those of the English Crag of which we now possess a very complete list.

If from the tertiary periods we pass down to the cretaceous, do we not find in the deposits of Mæstricht, or in those of the age of the white chalk, a number and variety of shells as great as that which may be found on any shore or in any circumscribed marine basin of an extent at all comparable with that of the cretaceous beds within similar limits? Do we not find in the lower cretaceous strata such as the green sand or the Neocomien, other assemblages of the remains of Mollusks, which, in number and variety, are not inferior to those of the white chalk? The oolitic series, again, will stand a similar comparison quite as well. We need not even take the whole group of those deposits, but consider each subdivision of the Jurassic period by itself, and still we find in every one, local fauna of Mollusks, assuming of course, a different character from those of the cretaceous or tertiary, but nevertheless sufficiently diversified to admit of an estimate, as advantageous, with respect to the points under consideration, and to the local fauna of the present day as to the cretaceous assemblages of fossils, or those of the tertiary period. Of course, in accordance with the peculiar character of the age, different families prevail in these different periods; the Cephalopoda are extremely numerous and surprisingly diversified during the cretaceous and oolitic periods; while they dwindle down to