108 T}>e Am<'r}can Geologixt. Fi-bmury, ww, 
sepanito IumiI (lescribinl as .1. itoniui/is. Tin* author remarks 
that the hitter (litiers in being "proportionately wider, the pos- 
terior bevelled margin thicker and the upper edge of the bevel 
rounded instead <jf lingular." which may 1>e due to age or other 
causes. The sides of .1. /irriK.scuJus are represented as quite 
smooth, but those of .1. nonniilla are obscurely ribbed. 
The pygidiuni of Ampyx rusfratus has a l)road, bevelled and 
striated limb. .Vxis faintly segmented with a row of nodes on 
each side, with tiie exception of the first segment, which is dis- 
tinct. The side l<)l)es have only one pair of anterior ribs. 
The following is the original description of the pygidium of A. 
iioninilis: Pygidium triangular, width twice the length, the two 
posterior sides gently convex, and the margin abruptly bent 
down or b;n'elled nearly vertically, the upper edge of the bevel 
angular and with indications of a slightly elevated linear rim; 
axis vi'ry dcpresseil. c-on\ex or nearly flat, its width at the an- 
terior margin about | of the whole width, extending the whole 
length or nearly so. crossi'd by obscure undulating furrows, 
.'^ide lol)es gently con\'ex. 
AM PYX RUTILIUS Billings, ISO.-). 
Compare Aiujiii.i i-iiiiroslatii.t liillings, 1865. 
DiiK/imsis. — Pygidium subtriangular. length about y^ of the 
width, nearly \-ertically lievelleil behind, the upper edge of the 
bevel with an acute linear rim. Axis C3'lindro-conical, strongly 
convex, (extending the whole length, with about 10 rounded 
rings. Side lobes nearly flat, slightly concave near the margin, 
Avith !t ribs very <listinctly detined the whole width. Width of 
the specimen 4 lines: length 1 .1 lines. 
Liirolitii. — Four iiiiles N. E. trbin I'orllaiid (reck, .Newfuiindlaud. 
- A(fiiiltlc^. — The .'lutlior remarks tiiut this species differs from Ampt/x 
si'iiiir<)xt(tfii-<. ill liuviiig- more numerous ribs which also extend the 
whole width. Il occurs along with it in the same beds. 
The j)ygidiuui of .l///y>//.( In rinsfulii^ differs from that of .1. nonnuUs 
in having a more prominent axis and a thicker posterior margin, also 
in being ])r(ii)ortioiiately wider. 
AMPYX SEMICOSTATUS Billings. 
DiinjiiiislK, — pygidium sub-triangular, [tosterior margin broadly 
rouiuled. obtusely angidar ;d the apex; length 2-5 of the width; 
axis cvlindro conical, stronolv convex extendino' the whohi 
