102 ROYAL SOCIETY OF CANADA 
narrow ridge at the chevron is seen in Tafl. 1, Fig. 81; but there is no 
opercule figured by Dr. Holm of the type of H. caudatus of the St. John 
Cambrian. 
Fig. F. Shows an opercule (Ordovician) of the second. type repre- 
sented in the St. John Group by H. Danianus. In the Bohemian oper- 
cule, however, the cardinal pits cover a shorter space transversely than 
in the Canadian. 
Figs. 14 &.15 (Cambrian). In this the several areas of the opercule 
are ouscurely shown only by radiate lines, the cone is not well defined. 
Fig. G. (Ordovician). Is a valve somewhat approaching the oper- 
cule of H. caudatus in form. | 
Fig. 20 (Ordovician). Decorticate opercule, shows mould of interior 
and thickness of the opercule at the chevron. The print of the cardinal 
muscle is rhombic with a shallow groove along the median line. The 
horizontal limb has two areas, one hollow near the chevron, the one 
behind, flat. 
Figs. 40-43 (Silur. & Ordov.) Show opercules that carry three areas, 
but no flat limb behind; 40-11 is conical, 42-43 semicircular and like 
an Orthis. They do not seem typical. 
PLATE 16, Fig. 4. Shows the cone striated all the way to the front, 
as in the preceding and in some examples of H. sericeus of the St. 
John group. 
PLATE 9, Figs. 16 & 17.{Ordov.) In this unusual form the cone is 
narrow and the lateral muscles double; the cardinal muscles cover a wide 
space laterally. 
MATTHEW. 
In the Cambrian Fauna of Mt. Stephen, B.C. [Trans. Roy. Soc. of 
Canada, New Series, vol. V., Sec. IV., 799, p. 39], the following are 
described: 
Plate I., Figs. 5a and b. H. carinatus. The tube in this species 
is elevated along the middle on the ventral side and limited by faint 
longitudinal ridges. The opercule referred to this species is very Acro- 
treta-like in the closeness of the apex of the cone to the ventral margin 
of the opercule; and in the strong lateral grooves (seen in the mould) 
delimiting the cone. 
In the Jllustrations of the Faunas of the St. John Group ['Trans. 
Roy. Soc. Can., vol. III., sec. TV., p. 55, pl. vi., fig. 7]. 
HYOLITHES SERICEUS. From the horizon 1d at Porter’s Brook. 
This form has a tenuous, shining shell, giving countenance to the view 
that Hyolithide are Pteropods. An example of the interior of the tube 

