Prof. E. J. Chapman on a new Species of Agelacrinites. 157 XXIV. — On a New Species of Agelacrinites, and on the Struc-tural Relations of that Genus. By E. J. Chapman, Professor of Mineralogy and Geology in University College, Toronto. Introductory Notice. — The accompanying figure represents, on a somewhat enlarged scale, the upper side of an undescribed species of Vanuxem's rare and interesting genus Agela-crinites, discovered amongst some Lower Silurian fossils from the Trenton Limestone of Peterborough, Canada West. It is dedicated to the able palaeontologist of the Geological A Survey of Canada, whose researches have so greatly added to our knowledge of the obscurer organisms of the Silurian age, and who has done so much, in all respects, for the advancement of Canadian palaeontology. The present communication is subdivided into two short sec-tions. The first contains a detailed description of the new species. This description, however, it should be remarked, is founded on a single example. The second section comprises an analytical review of the genus Agelacrinites in general, more especially with regard to its structural relations and affinities. 1. Description of Agelacrinites Billingsii. — Body circular, or nearly so. In the specimen on which this description is based, its diameter is exactly half an inch. It is slightly convex above, and flat, or apparently somewhat concave below. From the centre of the upper side, five rays, composed each of a double series of alternating or interlocking plates, radiate towards the margin of the disk, and terminate in well-defined points at about the twelfth of an inch from this margin. The rays, in the specimen under examination, exhibit no traces of pores, even when strongly magnified. Nevertheless pores may have been, and probably were, originally present. It is easy to conceive how minute orifices of this kind might become ob-literated during fossilization ; whilst, on the other hand, the object of the rays is altogether inexplicable, unless we look upon them as really representing ambulacral areas. Moreover, poriferous ray-plates have actually been discovered in certain examples of Agelacrinites; and analogy, consequently, would lead us to infer that they existed originally in all. These rays, at their origin, leave a small central space covered by larger and somewhat rhombic plates. The latter appear to be five in num-ber, and to constitute the first ray -plates, one being common to two adjacent rays. Very possibly, however, each of these rhombic plates may be divided through the centre, longitu-dinally ; for the specimen is much broken at this spot, and the plates are pressed, more or less, one over the other. The
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