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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. Cuapman, 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 palzontologist of the Geological 
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 paleontology. 
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 ali. 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 
Agelacrinites Billingsii, 
