18 
The mutual relations of the species of Melocrinus pertaining 
to the above correlated formations may be shown by the follow- 
ing analysis : 
alyx plates convex to sharply acuminate. 
Calyx elongate, higher than wide, with sides little curved. 
Plates low convex, frequently with small central spine on tnose 
of radial series, but these may be absent; basal plate s pro- 
jecting with sharp point or edge downward over' the top 
columnals; width of base to radial circlet is 9 to 13 mm. 
Specimens of medium 9ize M. tersus Rowley. 
Specimens small; central spine usually on both radial and 
interradial serijes, with centres connected by fine, radi- 
ating ridges. 
May be young of M. tersus M. lylii Rowley 
Spines relatively larger; basals not so sharply pro- 
jecting M. milwaukeensis Weller. 
Calyx rotund, or about same height and width; sides strongly con- 
vex. 
Plates of dorsal cup strongly tumid, bearing one or more small 
tubercles; tegmen plates numerous, flat, finely tuberculous; 
' basal plates strongly projecting; width of base to radial 
circlet as 6 to 11 mm. 
Specimens of medium size M. borealis n. sp. 
Plates of dorsal cup elevated into short, sharp spines. Calyx 
wider than high; height to width 35 to 39 mm.; expanding 
suddenly from base 13 mm. diameter to radial circlet 24 mm. 
Specimens large and robust M. gregeri Rowley 
Calyx plates flat 
Calyx rotund, higher than wide; sides strongly convex. 
Plates low, without connecting ridges, spines, or ornament. 
Specimens large M. canadensis n. sp. 
Compare also: M. calvini W. and Spr.; M. subglobosus 
Weller; M. nodosus Hall (Weller); M. nodosus var. 
spinosus Weller; M. milwaukeensis var. rotundus Weller. 
