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 



