pound eyes of insects. Its body is composed of several plates folding over each other, which, like the joints of the Lobster's tail, admit of considerable motion. They are prolonged laterally, so as to form a serrated edge to the body on each side. Its legs correspond to the number of the plates, at least of the projecting ones; and beneath the tail are a number of fringed appendages, which perform the office of gills. The Serolis is found on both shores of the Atlantic.

The next genus, Limulus, or King-crab (ibid., pl. 45, fig. 1), usually wants the antennæ, dorsal plates, and ribs of the Serolis ; Its body is formed of a shield, consisting of two plates jointed transversely the anterior semi-circular, the posterior triangular and terminated by a pointed tail, and its edges serrated and set with six spines on each side. It has four eyes-two compound close to the division of the shield, and two simple eyes, lying more in front, close to the median line. Its antennæ are very small; but it has twelve legs, and ten paddle gills. Its habitation is confined to the warm seas of India and America.

The third genus, Branchipus (ibid., pl. 45, fig. 4), is the animal with which many persons are familiar from its exhibition in the solar microscope, where its agility, voracity, and the extraordinary vibrations of its paddles and tail, while the body was at rest, were remarkably striking. It has no proper feet or legs, but its members, and even its tail, being fringed with gills, answer the purposes of organs of locomotion and respiration. It possesses antennæ, and inhabits fresh water.

Lastly, the Trilobite, (see plate, fig. 1), imperfect as it has hitherto been found, presents some of the characters of the two former genera, and, according to Brongniart, there is great reason to believe, of the latter also. Thus, it has the jointed body of the Serolis, and the large anterior plate or shield of the Limulus, and in some species the tail; but it has neither antennæ, legs, nor gills, though M. Brongniart conceives that it did possess the paddle gills of the Branchipus. Mr. Parkinson also believes that he has detected the existence of legs in one specimen, and M. Goldfuss gives some sections of a Calymene in which not only the presence of a ventral as well as a dorsal plate is clearly established, but also that of certain members, but whether these are legs or paddle-gills is not so evident. This account in vol. xv. of the Ann. des Sc. Nat., seems to have escaped the attention of English geologists, for Dr. Buckland says decidedly, that no Trilobite has been found possessed of legs All these classes of animals are aquatic.

or antennæ.

Trilobites consist of a thin oval plate of calcareous matter of various sizes, from half an inch to seven inches long, closely set with minute tubercles similar to those on the shell of the Crab. This plate is formed of many portions, the anterior of which, containing the eyes, is of a semicircular or crescent shape, and is called the shield; and to it are jointed a number of other plates like those on the Serolis, which, being crossed by two longitudinal grooves, together constitute a three-lobed tail, from which the fossil derives its name. The edge of the shell is turned inwards all round on the under surface, and hitherto no abdominal plate or members have been discovered. The eyes have been rarely found fixed in the shield, as they drop out, leaving an appearance of gaping eyelids. They are crescent-shaped, with the convex surface directed outwards, and are compound, as in the above-named genera, consisting of about four hundred facets or ocelli. From the close resemblance in the structure of the eyes of these animals, Dr. Buckland takes occasion to remark upon the permanence of the laws of nature from the earliest periods of which Geology supplies us with the records, when the earth was not yet fitted for the habitation of any animals higher than reptiles in the scale of organization, to the present time, when the earth teems with beings made in the image of the Creator, and but little lower than the angels.

In this neighbourhood shields and tails of Trilobites are very abundant in the thin upper layers of the Dudley limestone, but the finer and more perfect specimens are chiefly found in the lower and thicker beds. They are also met with in ironstone nodules at Coalbrook Dale.

Trilobites have been divided, by M. Brongniart, into five genera, which M. Latreille has distributed into three groups, viz., reniform or kidney-shaped, T. agnostus; contractile or folded, T. calymene; and extended or flat, T. asaphus, T. ogyges, and T. paradoxoides. Agnostus is of a semicircular shape; calymene rolls itself up like a Wood Louse, and its segments are not extended laterally; asaphus has a lengthened tail (see Bridgewater Treatise, pl. 46, fig. 11); ogyges has a long shield extended backwards on each side to a point (ibid., pl. 46, fig. 9); and paradoxoides has no appearance of eyes, and its plates are extended over the side, like those of Serolis (ibid., pl. 46, fig. 8).

Such are the chief generic characters of the Trilobite family given by Cuvier (Règne Animal, t. iv.), but they are not very distinct; and Dr. Buckland has recently added Limulus (Agnostus?) to them by the name of Limulus trilobitoides (ibid., pl. 462,

fig. 3). The number of genera hitherto described are 10, and of speecies 52. The specimen I now describe (see plate, figs. 2—3) seems to combine the characters of Serolis, Limulus, Agnostus, and Paradoxoides, with others peculiar to itself. It is enclosed in an ironstone nodule from Prior's Lee, in Shropshire, where the strata are far richer in organic remains, both animal and vegetable, than the Staffordshire coal basin, and it was from thence that Dr. Buckland's Limulus was derived. Some vegetable remains are visible on the exterior of the nodule. The accompanying figure is of the natural size. The lime, as in most calcareous fossils enclosed in ironstone, is in a crumbling powdery state, and is left white in the figure. The antennæ are very distinct, but the central anterior projection is not clearly defined, although, like the antennæ, it has a kind of tubercle at its base. The ribs or plates, with their lateral prolongations, are very evident; the two anterior being connected by a web into a kind of fin, which is readily distinguished from the prolongation of the shield observable in Limulus, Ogyges, and Paradoxoides. The surface of the specimen, from which the lime has crumbled away, is covered by minute crystals, and does not exhibit the tuberculated appearance of the surface of the Trilobites. The lateral projections are slightly grooved, and taper to a point. There is no appearance of eyes in either of the two specimens I have seen, unless the central projection is considered as such. The last of the elevated dorsal segments is remarkably prominent, and is quite distinct from the tail. The number of segments is six, extended laterally into as many ribs, terminated by a like number of legs, or more probably fin-rays or spines, for they exhibit no traces of a jointed structure.

Thus, in possessing antennæ it resembled the Serolis; it had a tail and lateral spines like the Asaphus and Limulus; its shape was that of Agnostus-i. e. extended laterally, not lengthwise; and it was devoid of eyes like Paradoxoides; which it also approached in the extended points of its shield. Judging from a note of Cuvier (Règne Animal, t. iv., p. 204), it closely resembles the description of the Paradoxoides of Rasoumowski.

The figure, (No. 4), is taken from an imperfect specimen of the shield of a crustaceous animal from the Dudley limestone. The spine or antenna is very distinct, but the other parts, having been much rubbed, are restored, as far as possible, from the cast. Its shape is that of a rounded oblong, arched and mammillated, and having an elevated margin; the whole surface, except the antennæ, is covered with the same minute tubercles that are observed on the