EMERY VULCANITE SAW GUMMER.
The vulcanite emery wheels made by the New York Belting and Packing Company have especial advantages for this kind of work. They are strong and safe at the highest speed at which it is desirable to run them, the company recommending that they never be run at a less rate than 6,000 feet per minute circumferential speed, and from that up to 8,000 and 10,000 feet per minute, although the lowest named speed is rather above the ordinary limit of many other kinds of emery wheels, and attempts to run other wheels at or beyond this limit have frequently resulted in serious accidents, from the breaking of the wheels. The higher rate of speed, which not only cuts faster, but, in the case of the vulcanite emery wheel, prolongs the life of the wheel, is concededly safe with the vulcanite wheel. Thus run, it is not likely to wear out of true, the operator does not have to bear on so hard, and the wheel retains its shape much better than when run at a slow speed. The nature of the wear of the working surface in the vulcanite wheel is claimed to be essentially different from that in wheels where the emery is fixed in its place by other methods, the rubber affording an elastic foundation or cushion, from which the particles of emery slightly protrude. This not only insures more efficient work from the cutting edges of the emery, as they become changed by use, but allows of more access of air to the work, thus tending to prevent casehardening of the edges of the metal being ground.
In addition to wheels with bevel shaped grinding surfaces, as represented in the engraving, the company also make wheels with round grinding surfaces, and this kind is always considered best for large saws.
THE FRILLED SHARK—THE OLDEST LIVING TYPE OF VERTEBRATES.
In technical terms this is a living species of cladodont shark, named by Mr. Garman Chlamydoselachus anguineus.
The specimen here figured was found in a miscellaneous collection of fishes, etc., in alcohol, furnished the Museum of Comparative Zoology by Professor H. A. Ward, who purchased them in Japan. It was soon recognized as not only belonging to a new family, but one closely allied to certain forms supposed to have become extinct in the Carboniferous time. This discovery displaces Ceratodus from the position of the oldest living type of the vertebrata.
The term Chlamydoselachus is applied on account of the curious frill-like mantle that surmounts the first gill cover. The term is made up of two Greek words implying mantle and shark. Six gill openings, and certain structure of the brain, remove this form from the present known sharks. Its affinity to some of the earliest known sharks, those of the middle Devonian, render it of great interest and importance to science. The family characters which this form represents, under the term Chlamydoselachidæ, are: Body elongate, with a depressed head. The eyes are lateral, with no nictitating membrane. The nasal cavity is separate from that of the mouth. The mouth is situated anteriorly, like that of some fishes. The teeth have broad, backward extended bases and slender cusps. The spiracles are present. One dorsal fin, spineless, is present. There is also an anal fin, and a caudal with no pit at its root. The first gill cover is free across the isthmus. The intestine has a spiral valve.
The generic characters are: Six gill openings, opercular flap, first gill cover, broad. Teeth similar in both jaws; each with three slender, curved, subconical cusps, separated by a pair of rudimentary denticles or a broad base. There is no median upper series of teeth in front, but there is a series below, on the symphysis. The mouth is wide, and has no labial folds at the angles. The pupil is horizontally elongate; the fins are broad, the caudal without a notch.
The total length of this shark is nearly five feet. Its greatest width, across the ventrals, is seven inches. Its resemblance to a snake is very striking. Its elongated body, long, flattened head, anterior mouth, and sinister expression of the eyes are quite suggestive of the ophidians. There are fifty-one rows of teeth, and six teeth in each row; the whole number at one time in function is 306. The brain is very small.