592 NEW SPECIES OF CRINOIDEA, 
ridge extends over cach plate, and projects a little below its base. These ridges, which are more promi- 
nent inferiorly than superiorly, and wider from below upwards, receive the five ambulacra. Each of the 
ambulacra is divided into two equal parts by a longitudinal furrow, and each part is composed of a double 
series of minute, elongated, subhexagonal plates, articulating among themselves by a line of alternately 
salient and retreating angles. The number of little plates in each of the above spaces, amounts to about 
two hundred. These articulations are bounded externally by a longitudinal gutter, at the bottom of 
which a series of minute pores are perceptible by the aid of a good lens. The pores probably served for 
the transmission of small brachial ligaments, by which the delicate arms attached to their margins were 
set in motion.* 
Superior plates small, lanceolate, each one with a mammillary projection near the inner angle, perfo- 
rated at the summit by a minute rounded opening. 
It occurs in the subcarboniferous limestone at Burlington and Augusta, Iowa, and Oquawka, Illinois. 
We dedicate this elegant species of Pentremite to our highly esteemed and gifted friend and co-labourer, 
Dr. J. G. Norwood, of Madison, Indiana. 
PENTREMITES MELO. (N. 8.) 
(Tab. V. a, fig. 14, a, b,c.) 
The form of this Pentremite is globular, sometimes slightly elongated, and the surface is ornamented 
with minute granule, very regularly arranged in longitudinal rows as in the P. Norwoodii. 
Basal plate small, pentagonal, flat or slightly concave, composed of three pieces, two are broad penta- 
gonal, and oneis rhombic. The articulating surface for the column, which is round and equal to one- 
half the diameter of the plate, is finely striated on the margin, and exhibits a minute central perforation. 
The external edges of the plate are slightly concave, to accommodate the inferior rounded edges of the 
perisomic plates (costals of Miller). 
ese latter are of an elliptical form, convex, and project inferiorly a little below the plane of the 
basal plate, while their summits are truncated on both sides of the ambulacra for articulating with the 
superior plates. Their union is strongly marked by a deeply indented longitudinal furrow. The ambu- 
lacra are narrow, and widen slightly from below upwards; they commence from a half to three-quarters 
of a line above the basal edge of the plates, and are continued a little beyond their superior margins, 
_ more deeply inserted into the ambulacral gutter superiorly than inferiorly. The ambulacra are 
small plates, arranged as in the P. Norwoodii; these are marked on the edges by 
fine strize, which are perceptible only by the aid of a good lens. 
plates small, elongated, symmetrical, composed at the base of a truncated triangle, sur- 
mounted by an irregular hexagon. The inferior lateral edges of the hexagon in four of these plates are 
notched, so that when united to the contiguous ambulacra eight pores are formed, surrounding the sum- 
mit. The fifth superior plate is perforated with an oval opening—the vent—which is much larger than 
the above-mentioned pores. 
It occurs in the subcarboniferous limestone at Burlington, Iowa, where it is rather abundant. We 
have not observed it at any other locality. 
Dimensions.—Height, 6-5 lines; width, 6 lines; diameter of pelvis, 1:5 lines; length of perisomic 
plates, 6 lines; width of perisomic -plntak; 3 lines. 
PENTREMITES LATERNIFORMIS. (N. 8.) 
(Tab. V. a, fig. 15.) 
Of this species we possess only a siliceous mould of the interior, and it may hereafter, when more 
perfect specimens are found, originate a new genus; for the present, however, we will not separate it 
from the Pentremites. 
* Among a number of specimens of Pentremites florealis (Say), procured by J. Evans at Chester, Pune we 
have found one, in which the arms still remain attached, and lie folded in the ambulacral spaces. These 
extremely oes and originate at the so-called pores of the ambulacra. They are composed of abies plates 
arranged in longitudinal series, as in the true Crinoids. None of them bifurcate, and we hav 
observe any traces of tentacule. In the specimen the five apertures at the summit are completely closed by a conical 
abdominal integument, made up of small microscopic pentagonal plates. 
