[MATTHEW | ACROTHYRA AND HYOLITHES 105 
HYOoLITHES DANIANUS, Horizon 14 Porter’s Brook.1 Tube 3 x 13 
mm. Angle of aperture 1 to 4°3. Shows stiffening lateral ridges for 
one-half of its length. This species is slenderer and more regularly 
tapering than H. Acadicus. Another example 4 x 16 mm. angle of aper- 
ture 1 to 4; regular taper, apex flexed to one side, flexuous, shows vas- 
cular stiffening lines on each side for three-quarters of its length. 
A tube perhaps of this species from the same horizon as the above. 
Size 34 x 13 mm. angle of aperture 1 to 3°7; shell rigid from apex to a 
width 54 mm.; then diverging ridges appear on each side of dorsal face. 
HYOLITHES DANIANUS, OPERCULE. Same horizon and locality (Figs. 
1b). Longitudinal diameter 4 mm., transverse 44 mm. Mould of in- 
terior has a raised cone, wide, with a blunt apex; this cone merges be- 
hind into a wide horizontal limb; the cone has a somewhat elevated 
central quarter (or fifth) that is divided by a shallow median groove 
(1.e., a ridge on the inside of the opercule) deeper and narrower toward 
the apex, as in a brachiopod. The cone is bounded by a sharp, deep 
furrow (mould of a ridge on the inside of the opercule) that extends, 
deepening as it goes, to the flattened margin. 
Behind the umbo is a deep, lobed, transverse pit (ridge on the inside 
of the opercule) whose length is one-third of the transverse diameter 
of the opercule; this pit is deepest and largest at the end, where its 
extremities are turned backward and inward toward the posterior mar- 
gin, defining a somewhat raised area at the back of the opercule, like 
the cardinal process in a brachiopod. 
The ends of this groove would be opposite the median area of the 
ventral side of the tube of habitation. 
On the exterior the lateral ridges of the opercule are visible by 
their projection above the general level, but the transverse ridge at the 
back of the opercule is not thus indicated. 
HYOLITHES CAUDATUS,. Horizon 14 at Porter’s Brook.2 
Tube 14 x 9 mm., angle of aperture 1 to 6. Another tube 24 x 12 
mm., angle of aperture 1 to 4°8. The breadth of the second example 
is probably increased by pressure and flattening, This small species 
is distinguished by two striæ on each side of the median area on the 
ventral face. Usually also a stria on each side toward the margin of 
the dorsal face. Lip of dorsal gradually rounded (and rather high), 
and so not angulated at the corner of the lip. 
The tube in this species was round as is shown by the form of the 
opercule. 

1Trans. Royal Soc: Can., vol. III., sec. FV., p. 49, pl. vi., figs: 1, 10. 
MPrans EOYs SOC. Sank, Vol.) LIT Sec AIN Dubs. Din Wien) ese bs Das 
