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A central tube, the SIPHUNCLE, passed through from the body chamber to the closed tip of the cone. The seashells, both brachiopods and mollusks, are in some respects the most important to the geologist of all fossils.
On close examination, the saucer-shaped partitions were proved to be all perforated at one point, and the perforations being situated exactly in the same line, the chambers were seen to be traversed by a canal, or siphuncle, which thus connected the smallest or aphical chamber with the largest.
The dorsal position of the siphuncle, however, clearly distinguishes the Goniatite from the Nautilus, and proves it to have belonged to the family of the Ammonites, from which, indeed, some authors do not believe it to be generically distinct. Psammodus porosus, Agassiz. Bone-bed, Mountain Limestone. Cochliodus contortus, Agassiz. Bone-bed, Mountain Limestone.
It has altered the position of the siphuncle, has placed it in the centre instead of leaving it on the back, but it still whirls its spiral logarithmically as did the Ammonites in the earliest ages of the world's existence. And let us not run away with the idea that these princes of the Mollusc tribe have a monopoly of the scientific curve.
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