592 



NEW SPECIES OF CRINOIDE A, 



ridge extends over each 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. Gr. Norwood, of Madison, Indiana. 



\ 



PENTREMITES MELO. (N. S.) 

 (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 granules, very regularly arranged in longitudinal rows as in the P. Norwoodii. 



Basal plate small, pentagonal, fiat or slightly concave, composed of three pieces, two are broad penta- 

 gonal, and one is 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). 



These 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, 

 being more deeply inserted into the ambulacral gutter superiorly than inferiorly. The ambulacra are 

 composed of numerous small plates, arranged as in the P. Norwoodii; these are marked on the edges by 

 fine string, which are perceptible only by the aid of a good lens. 



Superior 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 plates, 8 lines. 



PENTREMITES LATERNIFORMIS. (N. S.) 

 (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, Illinois, we 

 have found one, in -which the arms still remain attached, and lie folded in the ambulacral spaces. These arms are 

 extremely delicate, and originate at the so-called pores of the ambulacra. They are composed of small plates 

 arranged in longitudinal series, as in the true Crinoids. None of them bifurcate, and we have not been able to 

 observe any traces of tentacuke. In the specimen the five apertures at the summit are completely closed by a conical 

 abdominal integument, made up of small microscopic pentagonal plates. 



