CANADIAN FOSSILS. 63 



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

 Fragments are not very uncommon, but perfect specimens exceed- 

 ingly rare. 



Collectors. — E. Billings, J. Kichardson, and others. The specimen 

 fig. 2 was found by Captain W. S. Hunter of Ottawa, and fig. 1 by 

 e! Billinss. 



Genus Amygdalocystites, Billings. 



{Canadian Journal, vol. ii. p. 270, 1854; Geol. Survey of Canada, Report, 1856, p. 288.) 



Generic Characters. — Body, ovate ; pelvis of three plates, above 

 which are eight or more irregular rows of plates ; the mouth is 

 near the summit, closed by a valvular apparatus ; arms, large, 

 recumbent, composed of a double series of joints bearing a single 

 row of pinnulae ; ambulacral orifice situated in the apex ; ambulacral 

 groove not in the centre of the upper surface of the arm, but on one 

 side ; column round; the plates are solid, or not poriferous. GrODeric 

 name from amygdale, an almond. 



Comarocystites differs from this genus by the possession of free arms 

 and the porous character of its plates. 



XI. Amygdalocystites floeealis, Billings. 

 Plate VI. Fig. la-le. 



{Canadian Journal, toI. ii. p. 270, 1854; Geol. Survey of Canada, Report, 1856, p. 289.) 



Description. — Body ovate, rounded at the apex, tapering towards 

 the base, about one inch and a-half in length. Each of the plates of 

 this species has a low rounded tubercle in the centre, from which 

 ridges radiate to the angles ; these ridges are scarcely elevated above 

 the surface where they leave the border of the tubercle in the centre, 

 but increase in width and height as they depart from it ; they are 

 sharp-edged, and attain their greatest height at the angles of the 

 plates. The arm crosses the summit, and extends nearly down 

 to the base upon one side, and only two or three lines from the 

 apex on the other ; it is composed of a series of large joints, 

 which are about one line in height and scarcely so much in width, 

 and a second series of smaller pieces about one-half the height which 

 are placed at the bottom of the larger, upon one side. The arm 

 thus composed forms a projecting ridge up the posterior side of the 

 body across the apex, and a short distance down the anterior side. 



