mining and studying the large collection of West Indian shells, marine and terrestrial, of corals, sponges, crustacea, semi-fossil shells of the island, made by the Governor, Mr. RAWSON. Of the marine series he wrote in the following terms to Mr. J. G. Anthony, the Curator of the Harvard Museum:-"I am having high carnival. I have found here what I did not expect to find anywhere in the world—a collection of shells in which the young are put up with as much care as the adult, and extensive series of specimens show the whole range of changes of the species, from the formation of the nucleus to the adult." He was particularly struck with the now unique specimen of Holopus, lately procured by Mr. RAWSON, which was described by Dr. J. E. Gray in the December number of the "Annals of Natural History," and named by him, from a drawing, H. Rawsoni, but which Agassiz, who had seen the specimen of D'Orbigny in Paris, before it disappeared, considers to be a normal specimen of H. Ranzii, which had only four, instead of five arms. Count Pourtales recognised among the corals several similar to those which he had obtained by dredging in or near the Gulf Stream, and described in the latest No. (4) of the "Illustrated Catalogue of the Museum of Comparative Zoology at Harvard College," the presence of which on the coast of Barbados serves to indicate the close similarity of submarine life in those two distant localities.

The next two days, or rather the night of the next, and the greater part of the following day, were spent in dredging in the neighbourhood, in a depth of 60 to 120 fathoms, about a mile. from the shore, whence Mr. RAWSON has procured his fine specimens of Pentacrinus Mülleri. The Holopus was found on the opposite side of the island. The results were beyond the expectations, or even the hopes, of the most sanguine of the party. Only dead fragments of the Pentacrinus were obtained, but among the abundant spoils were four specimens of a new genus of Crinoid, without arms on the stem, (like Rhizocrinus?) which remained alive, with the arms in motion, until noon on the following day, under the excited observation of the party. A number of deepsea corals, alive, crustacea, sea urchins of new species, star fish, sponges (crutaceous, jurassic,) and corallines, &c., and a rich harvest of shells, were obtained. Among these was a splendid live specimen of Pleurotomaria Quoyana, F and B, of which genus Chenu writes that only one living species, and of that only one specimen, is known. The animal exhibited remarkable affinities,

and the artist accompanying the expedition was able to take several sketches of it, A large Oniscia, shaped like O. cancellata Sow., but with an orange inner lip (0. Dennisoni?), some specimens of Phorus Indicus Gmel., a magnificent new species of Latiaxis, with many exquisite specimens of Pleurotoma, Fusus, Murex, Scalaria, .and three or four of Pedicularia sicula Sw., with innumerable Pteropods and Terebratulina, rewarded these "burglars of the deep." The Professor was delighted, and it was with reluctance he abandoned so rich a field in order to secure his passing through the Straits of Magellan at a right season.

Barbados, January 26,

-From "Nature,"

AGASSIZ'S DEEP-SEA EXPLORATIONS.-More about the trilobites. The following letter has been received by Prof. Peirce of Harvard College from Prof. Agassiz, giving interesting details respecting some of the results of the researches of the Hassler Expedition:

"RIO, ON BOARD THE HASSLER, Feb. 12, 1872. "MY DEAR PEIRCE,-On January 18, Pourtales dredged to a very late hour during the night, the weather being more favor able for this kind of work than it had been at any previous time since we left Boston. As I did not dare to remain exposed to the dew, I missed the most interesting part of the proceedings, about which Pourtales will report himself. The next morning,. however, I had an opportunity of overhauling the specimens. brought up by the dredge, and to my great delight I discovered among them another of those types of past ages, only found nowadays in deep water. The case is entirely new, as the specimen in question belongs to the Pectinidal, a family the relations of which to earlier geological formations have thus far presented nothing especially interesting or instructive, except perhaps the fact that the type of neither is exclusively cretaceous. I wish had within my reach the means of making a full statement of the facts; but I have not the necessary books of reference, and must in this case trust entirely to my memory.

Among the most remarkable species of Pecten, there is a very small one, figured in Goldfuss under the name of Pecten paradoxus, if I remember rightly, and found in the Lias of Germany, which I have always been inclined to consider as the type of a distinct genus on account of its structural peculiarities. As yet nothing

like it has been made known among the living shells. Now among the few specimens dredged on this occasion in 500 fathoms depth, off the mouth of the Rio Doce, there was one living specimen of the same type as the Pecten paradoxus, showing particularly, and very distinctly, the prominent radiating ribs rising on the inner surface of the shallow valve to which the fossil is indebted for its specific name. Like the fossil, the living species is of small dimensions, measuring hardly two-thirds of an inch. I hope I may be able to dissect the animal at some future time, and work out the anatomical character of this exceptional type. With it a few other shells, already known to us, from deep waters, were also found; among them, two beautiful species of Pleurotoma, identical with species found in Florida, off Barbados.

In my first letter to you concerning deep-sea dredging, you may have noticed the paragraph concerning crustacea, in which it is stated that among these animals we may expect "genera reminding us of some Amphipods and Isopods aping still more closely the Trilobites than Serolis." A specimen answering fully to this statement has actually been dredged in 45 fathoms, about 40 miles east of Cape Frio. It is a most curious animal. At first sight it looks like an ordinary Isopod, with a broad, short, flat body. Tested by the characters assigned to the leading groups of crustacea, whether we follow Milne Edwards, or Dana's classification, it can, however, be referred to no one of their orders or families. As I have not the works of the authors before me, I shall have to verify more carefully these statements hereafter, but I believe I can trust my first inspection. The general appearance of my new crustacean is very like that of Serolis, with this marked difference, however, that the thoracic rings are much more numerous and the abdomen or pygidium is much smaller. It cannot be referred to the Podopthalmians of Milne Edwards (which corresponds to the Decapods of Dana) because it has neither the structure of the mouth, nor the gills, nor the legs, nor the pedunculated eyes of this highest type of the crustacea; nor can it be referred to the Tetradecapods of Dana (which embrace Milne Edwards's Amphipods and Isopods), because it has more than seven pairs of thoracic limbs; it cannot be referred to the Entomostraca, because the thoracic are all provided with locomotive appendages of the same kind. But it has a very striking resemblance to the Trilobites; it is in fact, like the latter, one of those types, combining the characteristic structural features of

other independent groups which I have first distinguished under the name of synthetic types. Its resemblance to the Trilobites is unmistakable, and very striking. In the first place the head stands out distinct from the thoracic regions, as the buckler of Trilobites; and the large, kidney-shaped facetted eyes recall those of Calymene; moreover, there is a facial suture across the cheeks, as in Trilobites, so that, were it not for the presence of the antennæ, which project from the lower side of the anterior margin of the buckler, in two unequal pairs, these resemblances would amount to an absolute identity of structure. As it is, the pres ence of an hypostome, in the same position as that piece of the mouth is found in Trilobites, renders the similarity to this extinct type of crustacea still more striking, while the antennæ exhibit an unmistakable resemblance to the Isopods.

In view of the synthetic character of these structural features it should not be overlooked that the buckler of our new crustacean, for which I propose the name of Tomocaris Peircei, extends sideways into a tapering point, curved backward over the first thoracic ring, as is the case with a great many Trilobites. The thorax consists of nine rings, seven of which have prominent lateral points, curved backward, like the pleuræ of Olenus, Lichas, &c. The sixth ring is almost concealed between the fifth and seventh, and is destitute of lateral projections, as is also the ninth. These rings are distinctly divided into three nearly equal lobes by a fold or bend on each side of the middle region, so that the thorax has the characteristic appearance of that of the Trilobites, to which the latter owes its name. The legs are very slender, and resemble more those of the Copepods and Ostracoids than those of any other crustacea. There are nine pairs of them, all alike in structure, six of which, however, the anterior ones, are larger than the three last, which are also more approximated to each other. Besides the legs, there is a pair of maxillipeds attached to that part of the buckler which extends back of the facial suture. These maxillipeds resemble the claw of a Cyclops. All these appendages are inserted in that part of the rings corresponding to the bend of the thoracic lobes; so that, if there exists a real affinity between the Trilobites and our little crustacean, and their resemblance is not simply a case of analogy, we ought hereafter to look to a corresponding position for the insertion of the limbs of Trilobites. I do not remember with sufficient precision what Billings, Dana, and Verrill have

lately published concerning the limbs of Trilobites, to say now what bearing the facts described above may have upon the subject, as lately discussed in The Journal of Science. But of one thing I am satisfied, since I have examined the Tomocaris Peirceithat Trilobites are not any more closely related to the Phyllopods than to any other Entomostraca, or to the Isopods. In reality, the Trilobites are, like Tomocaris, a synthetic type, in which structural feature of the Tetradecapods are combined with characters of Entomostraca and other peculiarities essentially their

own.

The pygidium or abdomen of Tomocaris is very like the abdomen of the ordinary Isopods with an articulated oar attached sideways and leaf-like respiratory organs upon the under side. The whole pygidium is embraced between the last curved points of the side of the thorax. Owing to these various combinations, I would expect in Trilobites phyllopod-like respiratory appendages under the pygidium only, and slender, articulated legs, with lateral bristles under the thorax, so thin and articulated by so narrow a joint as easily to break off without leaving more than a puncture as an indication of their former presence. It is impossible to study carefully the synthetic types without casting a side glance at those natural groups, which, without being strictly synthetic themselves, have nevertheless characters capable of throwing light upon the whole subject. And in this connection I would say a few words of Apus and Limulus. If I remember rightly, Milne Edwards considers the shield of Limulus as a cephalothorax in which the function of chewing is devolved upon the legs, while he regards the middle region as an abdomen, and the sword-like tail as an appendage sui generis. In the light of what proceeds, I am rather inclined to consider the cephalic shield of Limulus as a buckler homologous to that of the Trilobites, and the middle region as a thorax in which the ring show unquestionably signs of a division into lobes as in Trilobites. The tail would then answer to the pygidium. Apus should be compared with the other crustacea, upon the same assumptions as Limulus.-Ever truly your friend, L. AGASSIZ.

-From the New York Tribune.

DREDGING IN LAKE SUPERIOR UNDER THE DIRECTION OF THE U. S. LAKE SURVEY.-Extensive dredgings were undertaken the past season in Lake Superior, from the U. S. steamer