Изображения страниц
PDF
EPUB
[ocr errors]

the pectinated rhombs of Cystideans, the tube apparatus of Pentrenites, and the sand-caval of Asterids. Messrs Meek and Worthen and Dr. Lütken, on the other hand, regard it as associated in some way with the alimentary canal and the function of nutrition.

The author strongly supported the latter opinion. The perivisceral membrane in Antedon and Pentacrinus already alluded to, which lines the whole calyx, and whose involutions, supporting the coils of the alimentary canal, contribute to the formation of the central columella, is crowded with miliary grains and small plates of carbonate of line; and a very slight modification would convert the whole into a delicate fenestrated calcareous plate. Some of the specimens in Mr. Wachsmuth's collection show the open reticulated tissue of the central coil continuous over the whole of the interior of the calyx, and rising on the walls of the vault, thus following almost exactly the course of the perivisceral membrane in the recent forms. In all likelihood, therefore, the internal calcareous network in the crinoids, whether rising into a convoluted plate or lining the cavity of the crinoid head, is simply a calcified condition of the perivisceral sac.

The author was inclined to agree with Mr. Rofe and Mr. Billings in attributing the functions of respiration to the pectinated rhombs of the Cystideans and the tube apparatus of the Blastoids. He did not see, however, that any equivalent arrangement was either necessary or probable in the crinoids with expanded arm, in which the provisions for respiration, in the form of tubular tentacles and respiratory films and lobes over the whole extent of the arms and pinnules, are so elaborate and complete.- Abstract of a paper read before the Royal Society of Edinburgh, by Prof. Wyville Thomson, April 3, 1871. From Nature.

ON THE SUPPOSED LEGS OF THE TRILOBITE, ASAPHUS PLATYCEPHALUS. By JAMES D. DANA.-(Am. Jour. Sci. May, 1871.) * At the request of Mr. E. Billings of Montreal, I have recently examined the specimen of Asaphus platycephalus be

• In the last number of this Journal, p. 227, an abstract from the Report of the Committee of the Brit. Association on Fossil Crustacea was published, and this paper should have appeared at the same time. In the March number of the Am. Jour. Sci., Prof. Dana bas given a second notice, in reply to Mr. Woodward, We shall publish them both together.

longing to the Canadian Geological Museum, which has been supposed to show remains of legs. Mr. Billings, while he has suspected the organs to be legs so far as to publish on the subject, * has done so with reserve, saying, in his paper, " that the first and all.important point to be decided, is whether or not the forms exhibited on its under side, were truly what they appeared to be, locomotive organs.” On account of his doubts, the specimen was submitted by him during the past year to the Geological Society of London ; and for the same reason, notwithstanding the corroboration there received, he offered to place the specimen in my hands for examination and report.

Besides giving the specimen an examination myself, I have submitted it also to Mr. A. E. Verrill, Prof. of Zoology in Yale College, who is well versed in the invertebrates, and to Mr. S. I Smith, assistant in the same department, and excellent in crustaceology and entomology. We have separately and together considered the character of the specimen, and while we have reached the same conclusion, we are to be regarded as independent judges. Our opinion has been submitted to Mr. Billings, and by his request it is here published.

The conclusion to which we have come is that the organs are not legs, but the semi-calcified arches in the membrane of the ventral surface to which the foliaceous appendages, or legs, were attached. Just such arches exist in the ventral surface of the Macroura, and to them the abdominal appendages are articulated.

This conclusion is sustained by the observation that in one part of the venter three consecutive parallel arches are distinctly connected by the intervening outer membrane of the venter, showing that the arches were plainly in the membrane, as only a calcified portion of it, and were not members moving free above it. This being the fact, it seems to set at rest the question as to the legs. We should add, however, that there is good reason for believing the supposed legs to have been such arches in their continuing of nearly uniform width almost or quite to the lateral margin of the animal; and in the additional fact, that, although curving forward in their course toward the margin, the successive arches are about equidistant or parallel, a regularity of position

• Q. J. Geol. Soc., No. 104, p. 479, 1870, with a plate giving a fullsized view of the under surface of the trilobite, a species that was over four inches in length.

not to be looked for in free-moving legs. The curve in these arches, although it implies a forward ventral extension on either side of the leg-bearing segments of the body, does not appear to afford any good reason for doubting the above conclusion. It is probable that the two prominences on each arch nearest the median line of the body, which are rather marked, were points of muscular attachment for the foliaceous appendage it supported.

With the exception of these arches, the under surface of the venter must have been delicately membranous, like that of the abdomen of a lobster or other macrouran. Unless the under surface were in the main fleshy, trilobites could not have rolled into a ball.

SUPPOSED LEGS OF TRILOBITES.--Mr. Henry Woodward, of the British Museum, in a reply to the paper by the writer in volume i, p. 320, of the present series of this Journal, supports the view that the supposed legs are real legs. He says that the remark that the calcified arches were plainly a calcified portion of the membrane or skin of the under surface is “an error, arising from the supposition that the matrix represented a part of the organism.” But Prof. Verrill, Mr. Smith and myself are confident that there is on the specimen an impression of the skin of the under surface, and that this surface extended and connected with the arches, so that all belonged distinctly together.

Moreover the arches are exceedingly slender, far too much so for the free legs of so large an animal; the diameter of the joints is hardly more than a sixteenth of an inch outside measure ; and hence there is no room inside for the required muscles. In fact, legs with such proportions do not belong to the class of Crustaceans. Moreover the shell (if it is the shell of a leg instead of a calcified arch) is relatively thick, and this makes the matter worse.

We still hold that the regular spacing of these arches along the under surface renders it very improbable that they were legs. Had they been closely crowded together, this argument would be of less weight; but while so very slender, they are a fourth of an inch apart. Mr, Wooward's comparison between the usual form of the arches in a Macrouran and that in the trilobite does not appear to us to prove anything. We therefore still believe that the specimen does not give us any knowledge of the actual legs of the trilobite. Mr. Woodward's paper is contained in vol. vii No. 7, of the Geological Magazine,

J. D. D.

3. NOTE ON THE DISCOVERY OF FOSSILS IN THE “ WINOOSKI MARBLE" AT SWANTON, VT.; by E. BILLINGS, F.G.S., Palæontologist of the Geol. Sury. Canada. —A few days ago Mr. Solon M. Allis, of Burlington, Vt., visited our museum and informed me that he had a specimen of the Winooski marble of Swanton which contained some fossils. Since then he has sent it to me: It contains, abundantly, a species of Salterella, which I believe to be the S. pulchella described in my Pal. Foss., vol. i, p. 18. This marble, both at Swanton and St. Albans, seems to underlie the Geologia slates. It is generally of a reddish, mottled color, but sometimes gray or greenish. The limestone at the straits of Belle Isle, in which S. pulchella is found, is also red, gray and greenish; and is, I have no doubt, of the same age. At this latter locality it overlies a red or brownish sandstone, conformably, which holds Scolithus linearis. I consider the Belle Isle sandstone to be the “ Quartz rock ” of the Green mountains of Vermont. In that case, the limestone at Belle Isle occupies, stratigraphically, the position of the Stockbridge limestone as represented by Dr. Emmons in his American Geology, part 2, p. 19. On page 19 of the same work, Dr. E., speaking of the Stockbridge limestone, says: “It is reddish at Williamston and is intimately blended with silex." In his Report on the Second Geological District of New York, in 1838, page 232, he gives a section of the rocks at Burlington combined with one of the strata at Port Kent. He there notices a gray limestone (at Burlington) of which he

says : :-" It is a stratum, which in Berkshire county, and other parts of the country, has generally been placed among the primary rocks; it is identical with the limestone at the base of Saddle mountain, and which covers more or less of the western flank of the Green Mountains." If the limestone to which he alludes is one of the gray varieties of the Winooski marble, then he is most probably right. I believe Mr. Allis's fossils are the first that have been found in the Winooski marble.

ZOOLOGY AND BOTANY.

DEEP-SEA DREDGING IN THE GULF OF ST. LAWRENCE.-The marine zoology of the deeper parts of the River and Gulf of the St. Lawrence has not been investigated until quite recently. This summer, under the auspices of the Natural History Society of Montreal, and in consequence of the kindness of the Hon. Peter Mitchell, Minister of Marine and Fisheries for the Dominion (who not only gave me facilities for dredging or board Government vessels, but also caused sufficient rope to be provided for the purpose), depths of from 50 to 250 fathoms were successfully examined. The greatest depth in the Gulf, to the west of the Island of Newfoundland, as given in the Admiralty charts, is 313 fathoms.

The cruise lasted five weeks, the first three of which were spent on board the Government shooner La Canadienne, and the remaining two on the Stella Maris. The area examined includes an entire circuit round the Island of Anticosti, and extends from Point des Monts (on the north shore of the St. Lawrence) to a spot about half way between the east end of Anticosti and the Bird Rocks. As these investigations were almost necessarily subordinate to the special duties on which the schooners were engaged, in several cases the same ground was gone over twice.

The bottom at great depths generally consists of a tough clayey mud, the surface of which is occasionally dotted with large stones. So far as I could judge, using an ordinary thermometer, the average temperature of this mud was about 37° to 389 Fahren. heit, at least on the north shore. In the deepest parts of the river, on the south shore, between Anticosti and part of the Gaspe Peninsula, the thermometer registered a few degrees higher. Sand dredged on the north shore in 25 fathoms also made the mercury sink to 37° to 38°.

Many interesting Foraminifera and Sponges were obtained, but as yet only a few of these have been examined with any care. number of Pennatulæ were dredged south of Anticosti; the genus has not been previously recorded, so far as I am aware, as inhabiting the Atlantic coast of America. They were found in mud, at depths of 160 and 200 fathoms, and it seems probable that this species, at least, is sedentary, and that it lives with a portion of the base of the stem rooted in the soft mud. Actinia dianthus and Tealia crassicornis were frequent in 200 to 250 fathoms. The Echinoderms characteristic of the greater depths are a Spa. tangus (specifically distinct from the common British species), Ctenodicus crispatus, Ophioglypha Sarcii (very large), Ophiacantha spinulosa, and Amphiura Holbollii. Marine worms, of many genera and species, were both numerous and fine. Among the more interesting of the Crustacea were Nymphon grossipes (?)

« ПредыдущаяПродолжить »