30 A POPULAR EXPOSITION OF THE 
questioned whether all the separated caudal-shields referred to that 
type, really belong to it.* The species are restricted, as far as present 
observation goes, to the lowest fossiliferous zone. 
Tilenus:—In this well-characterized genus, the shell-covering is 
more or less smooth and comparatively free from furrows. Head, 
thorax, and pygidium are in most specimens nearly equal in size. 
Glabella broad, but feebly raised or otherwise defined. Eyes far 
apart. Body-rings generally ten 
(rarely eight or nine) in number. 
Pygidium almost or quite smooth, 
with even, rounded outline. The 
genus belongs to both the Lower (7 == 
and Middle Silurian deposits, but <4 
is chiefly found in the ae and a : 
higher parts of the lower series. a 
Fig. 143 represents one of our 
most common species, from the 
Trenton and Hudson River groups. 
It is usually referred to J/l@nus crassicauda. A “‘rolled-up” ex- 
ample is shewn at a. 
Phacops:—Glabella largely developed, expanded anteriorly, and 
often granulated but not lobed. Facial-suture 
cutting the sides of the head-shield. Eyes 
strongly reticulated. Head-angles and pleure 
with rounded ends. Body-rings eleven in num- 
ber. Pygidium with rounded or entire outline. 
Range of genus, Lower Silurian to Devonian. 
Phacops bufo (fig. 144) from the Devonian 
beds of Western Canada, is one of our most 
characteristic and and best known species. 
Dalmannites :—Like Phacops, but with lobed 
glabella, head-angles extended into horns, and 
pointed or spinose pleuree. Pygidium also with 
more or less spimose margin, or otherwise terminating in a point or 
spine. Fig. 145 represents Dalmannites limulurus from the Niagara 
group. ‘The caudal spine, in many specimens, is broken off. 
— 
E—— 
——— 
CT; ti 
eG 
*The caudal-shield referred to Dikelocephalus magnificus (Can. Nat., Vol. V., p- 307) ap- 
pears to have equal if not greater claims to be placed under Ceraurus. 
