CRUSTACEA. 
213 
rical, the outer portion of the posterior slope being a little more convex than 
the inner. 
In the third plate the form is much as in the preceding, but is broader, 
the apex more central and not so strongly incurved, the antero-lateral slopes 
more conspicuous and the posterior slope narrow and unsymmetrical. 
The fourth plate is almost the reverse of the first in form; the posterior 
area is abbreviated, very narrow and slightly concave just beneath the 
elevated apex; the outer lateral slope is broad and Hat. Whether the 
plate bears a median carina and differs as widely in the size of its lateral 
faces as in the first plate, cannot be determined, as it is largely covered by 
the preceding plate of the range. 
The fifth plate is broken and its form cannot be satisfactorily determined. 
In the right vertical range the plates were evidently symmetrical with those 
of the left, but have been somewhat displaced from their normal position. 
The first is in place; the second has been pushed out of its place and is not 
apparent, unless it is represented by the upturned lower surface of a plate 
visible near the lower portion of the specimen lying beneath the other plates; 
the third plate is pushed backward so as to show the strongly carinate anterior 
surface of the fourth plate projecting beyond its anterior edge; beneath this 
lies also the anterior edge of the fifth plate, showing that it also is carinate; 
and back of them all lies the sixth plate with a posterior apex, truncate 
behind, lateral slopes broad, the outer being the broader, and separated from 
the inner by a carina. Although this plate does not appear in the left range 
it may be represented by a fragment lying beneath the inner edge of the 
fourth plate of that range. 
The axial range is composed of small plates having about one-third the 
diameter of those of the lateral ranges. These differ considerably in form, 
but appear to be bi-symmetrical. Three are to be seen in juxtaposition on 
the anterior portion of the specimen, and a fourth is displaced and lies be¬ 
hind the inner posterior edge of the fourth plate of left range. 
In addition to these three ranges of plates is a vertical row of spines, 
.which, whatever their normal position, lie in a more or less detached condi- 
