LYON—BLASTOIDEA. 631 
Geological position and Locality.—P. robustus has been 
obtained from a single locality only, in the marly shale beds 
» at some hundred natural sections into 
the third limestone and the beds above it for several miles to 
the east and south, are found only Bryozoa and Corals, with 
i 
occasionally separate joints and fragments of crinoidal col- 
umns, 
» 
of second radials, ,89,. Specimen medium size. 
PENTREMITES ANGULARIS, 0. Sp. 
(Plate XX., Fig. 3a, 3b, 3c.) 
? 
prominent. Second radials five, long, forked three- 
ine from both ends to the center ; 
the summit of the poral pieces. Pseudambulacral fiel 
broad, gradually expanding from below upwards; widest i 
the Summit of the interradial pieces, angularly depresse 
from the sides to the line dividing the field; center grows 
shallow below, gradually deepening toward the summit, form- 
ing a sha angular notch, which is deepest opposite the cen- 
7 
