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 Terebratulinæ, 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 favorable 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 anten næ, 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 picce 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 pleura 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 Entomostracæ, 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 Entomostracæ 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

Search, under the direction of Gen. C. B. Comstock, Superintendent of the Lake Survey. Dredging was carried on from the shallow waters, especially along the north shore, down to 169 fathoms, the deepest point known in the lake. In all the deeper parts of the lake, the bottom, as shown both by the dredging and by the soundings executed by the Survey, is covered with an uniform deposit of clay, or clayey mud, usually very soft and bluish or drab in color. Water brought from the bottom at many points was perfectly fresh; that from 169 fathoms gave no precipitate with nitrate of silver. The temperature, everywhere below 30 or 40 fathoms, varied very little from 39°, while at surface (at the time of the observations, during August) it varied from 50° to 55°. The fauna of the bottom corresponds with these physical conditions. In the shallow waters, the species vary with the varying character of the bottom, while below 30 to 40 fathoms, where the deep-water fauna properly begins, the species seem to be everywhere very uniformly distributed. The deep-water fauna, as might be expected from the unfavorable character of the bottom, is meager, and seems to be characterized rather by the absence of many of the shore species than by forms peculiar to itself. Some of the more interesting species occurring in deep water were Mysis relicta Lovén, at various depths from 4 to 159 fathoms; Pontoporeia affinis Lindst., at nearly every haul from the shallowest to the deepest; a small undescribed species of Pisidium, down to 159 fathoms; several forms of dipterous larvæ, allied to Chironomus, down to the same depth; several species of Lumbricoid worms, of the genera Tubifex, Sænuris, and an allied genus; and a species of Hydra, which was found from the shore down to 159 fathoms. Of these, the Mysis, Pontoporeia, and Pisidium are identical with species found by Dr. Stimpson in his dredging in Lake Michigan, a short account of which was published in the American Naturalist for September, 1870. The species of Mysis and Pontoporeia I am unable to distinguish from specimens from the Lake Wetter in Sweden. In the Swedish lakes, these species were associated with Idotœa entomon and Gammaracanthus loricatus, marine species, and were supposed by Lovén to have been derived from ancient marine species left in the lake basins by the recession of the ocean. The occurrence of these forms in Lake Superior, so far removed from the ocean, is certainly a very interesting fact in the geographical distribution of species, but one which I will not attempt to discuss