84 CANADIAN FOSSILS. 



Agelacrinites Dicksoni, Billings. 

 Plate VIII. Figs. 3, 3a, 4, 4a. 



{A. Dicksoni, Geological Survey of Canada, Report, 1856, page 294.) 



Description. — The diameter of this species is from three quarters of 

 an inch to an inch and a half; the rays are five in number, and con- 

 structed upon a plan somewhat different from that of E. Bigsbyi, 

 being bounded by two rows of small plates, which rise from the 

 surface and arch over the grooves. The upper ends of the plates on 

 one side meet those of the opposite side, in a line along the centre 

 of the ray, thus forming for each ray a sort of covered way. The 

 spaces between the rays are paved with numerous flat sub-imbrica- 

 ting plates. The specimens do not show the central aperture dis- 

 tinctly, but between two of the rays there is an orifice which appears 

 to have been surrounded by small plates. The width of the rays at 

 their bases is from one to two lines, according to the size of the 

 individual, and they taper uniformly to their extremities. In all the 

 specimens I have seen, the rays curve round to the right hand, if we 

 suppose that the side with the aperture is posterior. The marginal 

 plates of the rays do not appear to alternate regularly, as in some of 

 the figured species of this genus. 



There are two rows of small circular indentations on each side of 

 the rays, corresponding in their position to the ambulacral pores of 

 E. Bigsbyi, only that in the latter they are in the bottom of the 

 grooves. It cannot be ascertained whether they penetrate through 

 between the marginal plates or not. 



I have dedicated this species to Andrew Dickson, Esquire, of 

 Kingston, C. W., one of the best workers in the field of Canadian 

 geology. 



The first specimen was discovered by Dr. Bigsby at the Chau- 

 diere Falls, at Ottawa, in 1S22. 



Explanation of Figures. Plate VIII. 



Figure 4. — The original specimen discovered by Dr. Bigsby, and now in the 

 Museum of Practical Geology, Jermyn Street, London. 

 4a. — The same enlarged. 

 3. — View of a different specimen, in the collection of the Geological 



Survey of Canada. 

 3a. — The same enlarged. 



Locality and Formation. — City of Ottawa. Trenton limestone. 

 Collectors. — Dr. Bigsby, E. Billings. 



