104 ROYAL SOCIETY OF CANADA 
Another example has the apex 74 mm. from the front margin ; 
another with apex 74 mm. from the front has a transverse diam. of 10 
mm. Horizontal limb of another 2 mm. wide. In a fourth the trans- 
verse diam. of the cone is 8 mm. and the horizontal limb is 14 mm. wide. 
A fifth has the former part 7 mm. wide and the latter 14 mm. 
Of a similar form to the opercule of H. sericeus is that of H. excel- 
lens, Bill,t but of thicker substance; the cone, however, is proportion- 
ately narrower. I have no example showing the sculpturing of the 
interior. This opercule is of interest as showing the growth of the hori- 
zontal limb, by which the apex is drawn away from the posterior mar- 
gin. This corresponds with changes in the form of the tube by which 
the lateral angles are brought around to the ventral side of the tube 
and the tube becomes rounder. 
HyouitHes Acapicus, Horizon 14 Porters Brook? Tube 10 x 30, 
angle of aperture 1 to 3; at 8 x 5 mm. the.angle of aperture is 1 to 1-6, 
hence in the first third the tube widens rapidly. 
At 8 mm. from the apex, there is a median raised area 2 mm., 
representing the “callus” of the brachiopod, and defined by a sharp 
groove on one side. At 18 mm. from the apex the median area on the 
ventral side is 4 mm. wide, the tube here being 84 mm. wide. The 
height of the lip of the dorsal side is 3 mm. and the width 10 mm. A 
ridge on each side of the dorsal face of the tube swerving out to the 
angle of the lip, defines a thinner median part of the dorsal face ; 
these ridges correspond to similar ones on the opercule. 
HYOLITHES GRACILIS, Horizon 1¢, St. Martins, N.B.* This also shows 
variation in the angle of aperture. Part of the tube 26 mm. long, 3% 
mm. at the proximal and 64 at the distal end gives an angle of aperture 
of 1 to 9-5; actual meast. give aperture 1 to 9:2. A young tube (Fig. 
26) 29 mm. long, proximal end 14 distal 5 mm. has the angle of aper- 
bore abo vei; 
HYOLITHES GRACILLIMUS n. mut. Horizon 1¢ from Rodney St., St. 
John (West). Tube, distal end 17 mm. long, 24 mm. at proximal and 4 
mm. at distal end gives the unusual apertural angle of 1 to 13-6. This 
is the distal part of the tube; the proximal which is thicker and 13 mm. 
long, proximal end 14 mm., distal 24 mm., gives a smaller angle, viz., 
1 to 10-4. The supposed larval part of the tube, which is detached is 
14 mm. long, and tapers from 0 to 1} mm.; this again gives a narrow 
angle of 1 to 11°. 

1Trans. Roy. Soc. Can., 2nd Ser., vol. V., sec. IV., p. 115, pl. vii., figs. 3 
eowes 
Trans. Roy. Soc. Can., vol. III., sec. IV., p. 54, pl. vi., fig. 6. 
3Trans. Roy. Soc. Canada, vol. III., sec. IV., p. 50, pl. vi., fig. 2. 

