junction of the pieces ; both pieces are irregularly pentagonal, nearly of the 
same form; that on the right of the anal piece being a little the largest 
separated one from the other by a very minute anomalous piece, which 
rests on the center of the first radials between them; it is nearly round, 
and rises under the suture which marks the separation of the second rm 
dials, and is about one fourth the height of those pieces. 
Third radials, twenty; small, differing both in size and form; nearly 
as high as wide, divided into five groups, disposed on a curved line, the 
exterior pair of each group resting partly on the first radial es lars. | 
central — 
gins of the second radials. 
r specimens are weathered to such an extent that all surface matk- 
ings (if they ever existed) have been removed. # 
Summi e summit above the arms is divided into five fields, neatly 
being a little the 
second range of the five fields and with the wings, in the same manner © — 
P. depressus (nobis). The second range consists of three long penta 
pieces, in the field above the anal piece, and two to each of the others. 
of various forms. The articulating surface applied to our specimeD pe 
the junction with the body, curved both above and below, gradually rate 
ning to a point, five times as long as thick, broad on the upper suae 
