86 ~=—s R. P.. Whitfield—New Forms of Fossil Orustaceans 
The genus Dithyrocaris McCoy is described as having three 
longitudinal ridges on the carapace. is feature is seen only 
when the two valves are pressed open as in McCoy’s example, 
so as to present the appearance of one large plate; in which 
case the hinge-line forms the middle ridge. 
The third or rostral plate in Peltocaris, Caryocaris, Discino- 
caris and Aptychopsis, would appear to be quite analogous to 
the small rostral plate seen in Ceratiocaris, and supposed to 
exist in Dithyrocaris, and perhaps some others, but which is 
usually absent. It is possible many of the forms may have 
possessed this rostral plate, at least among those that are deeply 
notched in front when the valves are spread open. In this 
case they would as properly be considered as having three 
plates in the carapace as those grouped under section 7. The 
forms of this section are usually found with the carapace spread 
open on the rock, and are then circular and diveoid: but when 
in their natural position would have been more or less roof- 
shaped. 
Colpocaris Meek presents some features which raise a question 
as to its true affinities. The longitudinal crenulated line and 
the inflection of the supposed ventral border do not seem to 
be properly understood ; and I am of the opinion it may belong 
to a different group of Crustaceans. 
EcuINocARIS SUBLEVIS, 0. Sp. 
Carapace obliquely subovate in general outline, the height 
equal to two-thirds the length, widest and deepest behind the 
middle, the posterior portion projecting obliquely backward 
and downward beyond the extremity of the hinge-line; dorsal- 
line straight, forming a hinge-line two-thirds the length of the 
valve; outer margin of the valves, except on the dorsum, bor- 
dered by a narrow, slightly raised and thickened rim; anterior 
border nearly vertical from the extremity of the dorsal line, for 
about one-half the width of the valve, except a very slight round- 
ing backward to the hinge-line above; below it slopes abruptly 
backward to and along the basal line, and again more abruptly 
curving around the posterior end of the valve and Pauls to 
the extremity of the cardinal line; below which it is distinetl 
excavated. The portion of the valve which projects beyon 
the hinge is fate or quite equal to one-third the length of 
the valve. Surface of the valves convex, and marked by 
ridges and tubercles. The principal ridge commences at about 
the anterior third of the valve, and just above the middle, as 
an elevated, rounded and nearly vertical ridge; but soon bends 
somewhat abruptly, and is directed backward in a broad, sweep- 
ing curve, at less than one-third of the height of the valve from 
the lower margin, and gradually decreasing in strength ter- 
