Messrs. Editors of the American Naturalist:—In answer to your question in regard to the above communication, I would say that while fully concurring with Dr. Higgins in his high estimation of Mr. Wales' objectives, I am of the opinion that he (Dr. Higgins) has either made an error in his measurement of amplification (210 diameters with the No. 1 or A eyepiece) or that the 4-10th objective is very much underrated in magnifying power. All of Mr. Wales' 4-10th objectives which I have seen have been as near or nearer 1-4ths than 4-10ths in magnifying power; and below I give a table of amplification of such 4-10th objectives as are at hand; also two 1-4ths for comparison: The measurements were made with a first-class stand and eye-pieces of Zentmayer, the image of a stage micrometer being thrown down by a Spencer's camera lucida, and measured at just ten inches from the eye; cover adjustment for 125th cover glass. It seems to me that there should be some uniform standard adopted by the different makers of objectives, so that the 1-4th of one maker may not be as high as the 1-6th of another maker; or a 4-10th of one be as high as a 1-4th of another; or, still worse, a 3-inch objective of one maker of precisely the same power as a 2-inch of another maker, which was just the case with two objectives which I had about one year since. If the objectives did not differ any more than the first three in the above table it would be an improvement. The amplification which Dr. Higgins gives to his 4-10ths is as high as the highest 1-4th in the above table. — EDWIN BICKNELL, Salem. ANTHROPOLOGY. THE BONE CAVES OF GIBRALTER. -The four Genista Caves, Martin's Cave, St. Michael's Cave and some others, have yielded evidences of early man, in the form of osseous remains, associated with flint knives and flakes, stone axes, polished and chipped; worked bones, serving as skewers, arrowheads, needles and gouges; anklets or armlets of shell, hand-made pottery, querns, rubbing-stones and charcoal. With these were found remains of numerous animals, including Rhinoceros etruscus, Rh. leptorhinus § (extinct); Equus, Sus priscus (extinct); Sus scrofa, Cervus ela Those marked thus §, are abundant; and thus §§, very abundant. A single molar of Elephas antiquus was obtained many years since by the late Mr. James Smith, of Jordan Hill, in an old sea-beach (now demolished) at Europa Point, the southern extremity of the rock. phus, var. barbarus §, Cervus dama §, Bos (a large form), and Bos taurus §; two forms of Ibex, Capra Ægoceros §§; and also the common goat, Capra hircus; Lepus timidus, Lepus cuniculus §§, Mus rattus. Of the carnivora were determined Felis leopardus, Felis pardina, Felis serval, Hyæna brunnea, Canis vulpes, Ursus sp.; also remains of the common dolphin, numerous genera and species of birds, a species of tortoise and numerous remains of fishes, of which the tunny is most prominent. The remains are imbedded in red cave-earth and also in a black layer similar to that noticed in the caves of France and elsewhere. In many instances the organic remains have been carried down from one cavern to another at a lower level through long fissures, by the heavy autumnal floods which pour from the higher grounds down upon Windmill Hill plateau (where many of these ossiferous caves are situated), bringing with them the remains of the various animals which at an earlier period inhabited the thickly-wooded heights, now entirely destitute of trees and only covered at places by the little Chamærops humilis. Many human and animal remains, attributable to modern periods, have been also met with; but the older human remains are distinguished by peculiarities in the thigh bones which closely resemble those met with in the Cro-Magnon Cave. - Quarterly Journal of Science. ANSWERS TO CORRESPONDENTS. W. H. S., Hummelstown, Pa. - The "Canadian Naturalist" is published monthly at Quebec, $2 a year gold. Address M. l'Abbé Provancher, Quebec, Canada. C. J. S., St. Augustine, Fla. No. 1, Pinquicula lutea; 2, Nothing came with this number; 3. Amianthium angustifolium; 4. Lupinus diffusus; 5, Pinquicula pumila. See Chapman's Southern Flora. For naming, fair specimens should be sent, - not miser able and withered bits. J. L. L., Boston. - Specimens of various species of sea-anemones with two months. each surrounded by its circle of tentacles, have often been observed and recorded in Europe. I have seen several instances of this kind in our native Metridium marginatum. It is, however, to be regarded as an abnormal condition, and appears in many cases to have been caused by some injury, which has been healed, leaving two disks instead of one. Spontaneous division occurs normally, however, in allied coral animals, and a disk-shaped sea-anenome is formed in the West Indies which naturally has two mouths (Ricordea florida Duch. and Mich.).-A. E. V. W. H. S., Hummelstown, Pa. The shells sent are as follows, by your numbers: 1, Helix monodon Racket (Stenotrema); 2, Helix tridentata Say (Triodopsis); 3. Heliz alternata Say (Anguispira); 4. Helix bucculenta Gld. (Mesodon); 5, Helix albolabris Say (Mesodon); 6, 7, Anculosa dissimilis Say; 8, Goniobasis Virginica Say (Melanía); 9, Paludina decisa Say (Melantho); 10, Sphærium sulcatum Lam.; 11, Planorbis bicarinatus Say; 12, 13. Margaritana undulata Say; 14, Unio complanatus Sol.; 15, Anodonta edentula Say; 16, Anodonta fluviatilis Lea.-G. W. T., Jr. BOOKS RECEIVED. Quarterly Journal of Science. London. April, 1870. The Academy, London. No. 8. May. Science Gossip. London. April and May. American Entomologist and Botanist. St. Louis. Vol. 2, No. 6. April, 1870. The Entomologist's Monthly Magazine. London (monthly). From December, 1868, to March, 1870, inclusive. The Field. London. April 9, 16, 23. Harris on the Pig; Breeding, Rearing, Management and Improvement. By Joseph Harris. Illustrated. 12mo, cloth. Orange Judd & Co. New York. 1870. $1.50. Sketches of Creation; a Popular View of Some of the Grand Conclusions of the Sciences in reference to the History of Matter and of Life. By Alexander Winchell, LL. D., etc. With illustrations. 12mo, cloth, pp. 460. 1870. Harper & Brothers. New York. Ir is proposed to give some results of a summer's study on the incubation of the eggs of the Horse Foot Crab, and to connect those results with observations made in an acquaintance of several years with the animal in its native haunts, in the hope of thereby furnishing something towards a life-history of the species.* Among systematists this crustacean is known as Limulus Polyphemus. It bears also the popular names Horse Foot Crab, Horseshoe, and King Crab. In this article these names will be used as convenience may suggest. The King Crab delights in moderately deep water, say from two to six fathoms. Except in the case of the very young, which are probably carried thither by the tidal flow; *In October, 1869, the writer read a paper before the Zoological section of the New York Lyceum of Natural History, under the title "A Contribution to the Natural History of the King Crab," which contained the notes taken during the summer's investigation alluded to above. The article now appearing in the AMERICAN NATURALIST is taken mainly from that paper. - S. L. Entered according to Act of Congress, in the year 1870, by the PEABODY ACADEMY OF SCIENCE, in the Clerk's Office of the District Court of the District of Massachusetts. AMER. NATURALIST, VOL. IV. 33 (257) it never seeks the shallow waters, unless for the purpose of reproduction. It is emphatically a burrowing animal—living literally in the mud, into which it scoops or gouges its way with great facility. The anterior edge of its enormous cephalic shield is not unlike in form the sausage, or mincemeat knife of our kitchens (Pl. 3, Fig. 12). The upper shell of the animal is composed of three parts—the forward shield, which is greatly the larger, the posterior shield, and the long bayonet-shaped spine, or tail. In the burrowing operation the forward edge of the anterior shield is pressed downward, and shoved forward, the two shields being inflected, and the sharp point of the tail presenting the fulcrum as it pierces the mud, while underneath the feet are incessantly active, scratching up and pushing out the earth on both sides. There is a singular economy of force in this excavating action, for the alternate doubling up or inflecting, and straightening out of the two carapaces, with the pushing purchase exerted by the tail, accomplish both digging and subterranean progression. Hence the King Crab is worthy to be called the Marine Mole. The Limulus is carnivorous. Its food is the soft nereids, or sea worms; so that not only in its mode of burrowing for concealment, but also in its method of procuring food does it resemble that little burrowing mammal of the land. It is sometimes found held in a strange durance, with a limb entrapped between the valves of the quahog, or round clam, (Venus mercenaria). It is a pitiful sight to behold—a galley slave with limb confined to ball and chain-"as far from help as limbo is from bliss." The explanation is easy. The quahog too is a burrower, and Limulus has seized the projecting syphon of the mollusc, which being suddenly withdrawn, the less agile claw is jerked between the valves, and the same are closed. This, of course, would effectually entrap the limb. But here occurs just this strange fact, that a lobster or a crab would not long be held in such durance, but would give their custodian leg-bail; that is, would cast off, and desert the imprisoned limb, and in due time would reproduce the lost member. The position of the mouth, and the masticating process are so peculiar, that, a description should not be omitted. The King Crab has six pairs of feet; although by some, those constituting the extreme anterior pair are called antennæ, being greatly shorter than the others. The four pairs between this first pair, and the last pair, have a functional structure differing from the anterior and posterior pairs. Of these four pairs, the basal joint, or haunch, of each limb is flattened and smooth on each side, as though they were a series of plates intended to work upon each other, as the keys of an organ under the fingers of the musician. The external edge of each is rounded, and beveled like the edge of a carpenter's chisel. Thus these flattened haunches lie against each other, their rounded edges directed backward at a considerable angle. The beveled edges (which are the exposed parts) of these projections are covered with very sharp incurved spines, overhanging and pointing into the oral aperture; for it is between these four pairs of spineclad haunches that the creature's mouth is situated. Each of these basal spines is articulated, and is set in the crater, or cup, of a little teat-like prominence. These then, are the true jaws of the animal's mouth; and as there are four pairs of these manducatory joints, the creature's mouth is set in a line between eight jaws. These spiny teeth have, by their articulation, an amount of mobility in their little pits, which is eminently serviceable and preservative. Of these chewing teeth, though the number is variable, an individual can scarcely have less than one hundred and fifty. Wishing to see what their food might be, and how they eat it, I placed a specimen, hatched the preceding summer, in a small aquarium, and supplied it with plenty of fresh and tender sea lettuce (Ulva latissima). But this sea salad remained untouched, although the young Limulus had no other fare for three weeks. In fact, famishment had rendered it |