634 TRANS. OF THE ACAD. OF SCIENCE. 
pyriformis, Say, especially to some of the shorter specimens 
of that species; from these it differs in the length of the ba- 
sal pieces ; in the less prominence of the pieces which form 
the boundary of the pseudambulacral fields, and particularly 
in the size and disposition of the poral pieces in the areas. 
The poral pieces in our. specimen number sixty-three in the 
sixteenth of an inch, or 105 to the inch. LP. elegans is also 
much more expanded at the lower extremity of the furcation 
of the second radials. 
In the size and arrangement of the poral pieces, it resembles 
a species which is probably referable to P. symmetricus (Hall’s 
Iowa Report). The excellence of its preservation, the beau- 
ty of its form, and the delicacy of its structure, are suggestive 
of its name 
Geological position and Locality —A few specimens have 
been obtained from the third limestone of the Millstone-gnit 
beds near Grayson springs, and at the summit of the ridge 
between Little Clifty and Rough Creeks, three miles north of 
Litchfield, Grayson County, Ky. At both localities they were 
found in aluminous shale near the top of the bed, although it 
has not been found in places in the rocks or shale ; its vertical 
range is presumed to be quite limited. It does not exist (?) 
below the horizon to which it is here referred, and Pentre- 
mites has not been found above the top of the third lime 
stone and shale beds associated with it, or its equivalent. 
Our species is rare, and is one of the last representatives of 
its race in its locality. .P. robustus occupies the same hor 
zon, and, like P. elegans, it has not been found associated 
with other species. : 
Size of Specimen.—Greatest vertical length, 1 inch; great- 
est diameter, 73; ; greatest length of pseudambulacral areas, 
est length of basal pieces, ;1°5; greatest length of first ra 
EXPLANATION OF PLATE. 
Plate XX. Fig. 1 —Pentremites calycinus. 
ole 1eW. 
“""' } ¢.—Basal -View. 
« 2 -—Pentremites robustus. 
6.2 a.—Profile.. Vi 
ck b.—Summit View 
© 2 ¢.—Basal View. é 
“ 3 —Pentremites angularis. 
Vj 
“ 8c¢—Summit View. 
“4 —Pentremites elegans. 
“ 4 6.—Profile View. 
“* 4¢—Summit View. 
