MINERALS AND GEOLOGY OF CANADA. 29 
horned head-shield, is also common in the Trenton Limestone of 
Cobourg, C.W. The genus asaphus, both on this Continent and in 
Fig. 140. Fig. 141. 
Europe, does not pass out of the Lower Silurian series. Examples 
vary in length from less than an inch to over eighteen or twenty 
inches. 
Ogygia:—This genus resembles Asaphus in its general aspect, 
number of body-rings, &c., but possesses an oval in place of a forked 
hypostoma. It is often impossible to decide, consequently, as to 
which genus fragmentary examples should be referred. Under Ogygia, 
the Dikelocephalus of Dale Owen, and the Bathyurus of Billings, 
should probably be placed. Several species of these, although in a 
more or less imperfect condition, have been found in the Quebec 
group (see Parr V.) of Point Levi, and also, as regards Bathyurus, in 
the corresponding Calciferous Sand Rock of the Mingan Islands, as well 
as in the Chazy Limestone of Grenville, &c. The body-rings in the lat- 
ter type are perhaps nine in number, but few specimens, in which they 
are complete, have as yet been met 
with. Fig. 142 represents a frag- 
mentary example of B. Angelini, 
after a figure by Mr. Billings, from 
the Chazy limestone. A portion 
of the head-shield of B. Saffordi, 
copied also from Billings, is shewn 
at a. In Dikelocephalus, the py- 
gidium has often a deeply serrated or spinose margin ; but it may be 
Fig. 142, 
