claws are compressed and pointed, figure 90, but at the same time slightly fissured at their extremities. 90 Although the magnum, trapezoid, and centrale are missing, the distal articular facets of the lunar render it certain that the position of the centrale was entirely under the scaphoid, as in Hyænodon. In this conFIGURE 90.-Termi- nection, I wish to call attention to a speci nal phalanx of fore- men of Hyanodon in the present collection, foot of Sinopa agilis which agrees very closely with H. crucians Marsh; three halves of Leidy. A portion of the carpus is prenatural size. (Type.) served, and it is of much interest to note that the scaphoid, lunar, and centrale, figure 91, are coössified, with the remains of the sutures still visible. This carpus differs from the one figured by Scott,* in that the lunar has a large contact with the unciform, and the centrale lies wholly upon the radial side of the lunar, under the Of the pelvic girdle, the ilium is FIGURE 91.-Coössified scaphoid, lunar, and cen- scaphoid. trale, of Hyænodon crucians Leidy; natural size. a, top view; b, front view; c, inner view. considerably expanded, and has a strong downward and outward curvature, as in Iyanodon; the peduncle is short and the tubercle for the rectus is large and rugose. The ischium is elongate and slightly expanded at its distal end. The pubis is not preserved. The femur has a strong resemblance to that of Ilyanodon; the hemispherical head is supported by a moderately short, stout neck; the fovea is distinct, the digital fossa deep, and the major trochanter rises almost to a level with the head; the trochanter minor is large, and the third trochanter is distinct and placed at a considerable distance down the shaft. The distal end of the bone exhibits the characteristic thickening of the lower end of the shaft, just before joining the condyles, as well as the general clumsy appearance seen in Hyanodon. The patella is relatively small, elongate, and narrow. tibia, figures 92–93, is also markedly Hyænodont in character. The enemial crest extends more than half-way down the shaft; the internal malleolus is large, and the trochlea is little grooved. The fibula is not so much reduced as it is in Hyanodon, but, as in that genus, there is a large contact with the calcaneum. The calcaneum, figure 94, has a moderately elongated tuber, and very convex astragalar and concave sustentacular facets. *Jour. Acad. Nat. Sci., Phila., 1886. The The astragalus, figure 95, has a rather obliquely placed, vertically flattened, rounded head, a slightly grooved trochlea, and a vertical fibular facet. The astragalar foramen is distinct and FIGURES 92, 93.-Left tibia of Sinopa agilis Marsh; front and end views; three-fourths natural size. (Cotype.) FIGURE 94.-Left calcaneum of Sinopa agilis Marsh; dorsal view; one and one-eighth natural size. (Type.) FIGURE 95.-Left astragalus of Sinopa agilis Marsh; dorsal view; one and one-eighth natural size. (Type.) occupies its usual position. unknown. The remainder of the pes is The principal measurements are given herewith: Measurements of the Type. Length of superior molar and premolar series, including Length of superior molar and fourth premolar 68-mm 29. 9. 9. 8. Transverse diameter of second molar Transverse diameter of third molar. Length of inferior molar and premolar series, from posterior base of canine... Length of inferior molars. Antero-posterior diameter of first molar crown. Antero-posterior diameter of third molar (not type) Length of humerus Length of third metacarpal. Length of first phalanx, third digit. Length of second phalanx, third digit Length of claw, third digit. Length of sacrum Transverse diameter of sacrum Length of pelvis (estimated). 3.mm 5.5 7. 9. 8. 66' 24. 7.5 9. 8.5 74. 113.5 32. 16. 10. 9. 49. 27. 128 Width of palate at and including second molars Length from incisive border to termination of palate. Measurements of the Church Buttes Specimen. Total length of cranium.. 149.mm 81. 68. 23. 40.5 The type specimen was discovered by Professor Marsh, at Grizzly Buttes, and the cotype by R. Son, at Church Buttes, Bridger Basin, Wyoming. [To be continued.] ART. XXXVII.—The Transmission of Sound through Solid Walls; by F. L. TUFTS, PH.D. IN a previous article* the author gave the results of some experiments on the transmission of sound through materials pervious to air, and it was shown that such materials behave in the same way with respect to sound transmission and to the flow of air currents through them. In the present paper experiments are described which were undertaken for the purpose of studying the transmission of sound through materials impervious to air. On account of the increased noisiness of cities and the desirability of excluding these noises from offices and dwellings, a knowledge of the laws governing the transmission of sound through various materials is becoming daily of greater importance, and the present investigation was, in fact, suggested by certain difficulties which had been encountered in excluding noises from telephone booths. The experiments, described below, were undertaken for the purpose of ascertaining the essential qualities which a wall must possess in order to render it impervious to the sound waves transmitted to it from the air. Consider, for example, a sound wave traveling in air, and suppose it to impinge upon a solid wall; there are three conceivable ways in which the sound may be propagated through the wall to the air on the other side: First, if the wall is pervious to air, the sound may be transmitted through the air in the pores of the material. The laws governing this kind of transmission were investigated in the previous paper. Second, if the material is impervious to air, the sound may be transmitted as an elastic wave in the material of the wall; or, Third, the pressure of the sound wave against the wall may produce a slight displacement of it, and the sound may thus be transmitted as a vibration of the wall itself. The apparatus used in studying the transmission of sound from the air on one side of an impervious wall, to the air on the opposite side, is shown in cross section in Fig. 1. A and B are two three-inch "gas unions," each fitted at one end with a "bushing" which reduces the opening to one inch. In these bushings, respectively, are screwed pieces of one inch gas pipe, a and b, about one foot in length. Rubber tubes, c and d, are passed through these pipes and are cemented in at their ends with beeswax. The rubber tubes are connected to This Journal, vol. xi, May, 1901, page 357. AM. JOUR. SCI.-FOURTH SERIES, VOL. XIII, No. 78. -JUNE, 1902. a T-tube at g. One arm of the T-tube is provided with an ear piece, h, which can be inserted in the ear of the observer. The iron pipes, a and b, were inserted in openings in an eightinch brick wall, and the observer could thus be placed in a room adjoining the one in which the sound was produced. The materials, the transmission of sound through which was to be investigated, were cut into discs about 10.5cm in diameter, and clamped in the unions at i and j, respectively. The application of a little cement rendered the junction air tight. Various sources of sound were used in these experiments, |