OF DENISON UNIVERSITY. 
57 
of its breadth at the proximal border, but diminishes very rapidly, ter- 
minating in a somewhat blunt point near the posterior margin, About 
14 somites, with about 9 plurae, surrounded by a narrow, smooth bor- 
der. The pigidium is more triangular that of P. colei. 
P. minor is a very small species, having a pigidium resembling 
that of P. eichwaldi. Head shield rounded in front, one-third broader 
than long; glabella occupying one-third breadth, oval, slightly broader 
in front, tumid, with distinctly marked basal lobes; lateral furrow in- 
distinct ; neck-lobe rather prominent ; angle of cheek produced into a 
short slightly curved spine. 
P. qiiadrilimha is too imperfectly described to be recognized and 
might better be dropped from synonomy. 
Griffithides brevispiims is known only from two fragments of the 
head. The author describes as follows : 
“ Head nearly twice as broad as long ; free cheek, terminating 
laterally in a short spine ; the eye, which is very smooth, is rounder 
and more tumid than ‘in other species. The glabella is nearly smooth 
in front, and overhangs the anterior border of head-shield ; posterior 
portion of the glabella and the neck-lobe irregularly tuberculated ; free 
cheek also tuberculated, about 8 tubercles on each cheek, placed in a 
semicircle about the eyes. Margin of shield. raised and striated.” 
G. I carringtqnensis is represented by pigidia resembling very 
much that of G. obsoletus, except that this species has 12 axial seg- 
ments and has a distinct margin to the pigidium, while G. obsoleius has 
but 10 segments. 
G. obsoleius. Pigidium one-fourth broader than long, composed 
of 10 segments, oxis much broader than plural portion ; each of the 
9 rib-like plicae marked by a furrow down the centre, margin smooth. 
Glabella covered with peculiar striations. 
G. plaiyceps was described from a fragmentary glabella, only and 
is not recognizable. 
The two species of Bi'achymetopus., B. discors and B. hibernicus 
are founded on pigidia only and the outline drawings given will afford 
all the information we possess concerning them. 
Meek’s Pliilllpsia lodiensis., if a Brachymetopus, is the only mem- 
ber of this genus yet found in America. 
We have thus hastily reviewed the exotic species and turn to a 
more careful study of the American forms. In the first place, let us 
examine the original descriptions. 
