WHITEAVES.] FOSSILS OF HiiMILTON FORMATION OP ONTARIO. 105 



outward. Oral side not quite thi'ee times as high u:s the ab-oral, of 

 nearlj' equal thickness for about one-third of its height, then narrow- 

 ing gradual]}' and convexlj' upward> from about the middle of the 

 calyx to the summit : peristome narrow and coneaveiy excavated. 



Basals reaching rather more than halt-way to the buses of the 

 radial sinuses, and together forming a rather shallow cup, which is 

 three-sided below, five-sided above and anguhirly five-lobed at its 

 upper margin, and whose breadth alcove i^ nearly twice its height. 

 Basal plates three, two pentagonal and one quadrangular. 



The " bodies " or undivided portions of the radials broaden outwards 

 more rapidly than the basuls do, and from this circumstance it follows 

 tliat an obtuse angle is formed at the junction of the basals with the 

 radials, especially in a line with the ambulacra. 



Eadials occupying about eleven-thii-teenths of the enlii-e height of 

 the calyx, lanceolate in outline, with a truncated base, and rather more 

 than twice as high as broad. The apices of each of the two adjacent 

 radials are united so as to form an acute point, which projects a little 

 above the oro-anal surface. Radial sinuses very deeply cleft, and 

 occupying about nine-tenths of the total height of each radial. The 

 sides bordering the sinuses are elevated and formed into sharp edges, 

 which stand out at right angles above the ambulacra in such a way as 

 to form prominent radial lips, which are somewhat effuse and most 

 raised around the bases of the ambulacra. 



Ambulacra linear, rather narrow, increasing in breadth regularly 

 but very slowly upwards, so that they are nearly twice as broad at 

 theii- summits as at their bases, which latter are narrowly rounded. 

 The food gi-oove in the centre of each ambulacrum deepens towards 

 the summit, and is almost obsolete at and near the base, while the 

 outer sides of the ambulacra are depi'essed in such a way as to form a 

 deep gi-oove on each side next to the radial lips. The whole surface 

 of each ambulacrum, although convex towards the centre, is not pr(j- 

 minent, but on the contrary sunk a little belmv the general level of 

 that of the radials. 



The interradial on the anal side is comparatively large, and plainly 

 visible in a side view, especially when examined with a lens ; its outline 

 is rhomboidal, but its apex is narrowly and rathei- ilceply emarginate. 

 The other interradials are extremely small, and not visible at all m a 

 side view, as they are sunk in the oro-anal excavation, and form a nar- 

 row rim ai-ound the spiracles. 



The posterior spiracle is confluent with the anal aperture. The 

 other spiracles (four in number) are rather lai-ge, between crescentic 

 and reniform in outline, rounded on their innci- margins, and placed 

 close to the central opening. They are situated within the inter- 



