64 OWEN AND SHUMARD'S FOSSIL CRINOIDEA. 



surface, which is somewhat of a semilunar shape, and slightly concave for the 

 insertion of the arms. 



Column, arms, and abdominal plates undiscovered. It is associated with the 

 preceding species at Burlington, where it is exceeedingly rare; only a single 

 specimen having rewarded our search. 



Genus PENTREMITES, Smj. 



Pentremites Norwoodii. (New sp.) 



PL 7, fig. 13, a, b, c. 



The general form of this species is globose, and the whole surface between the so- 

 called ambulacral spaces is thickly studded with small granulse, very regularly 

 arranged in longitudinal rows. At the base a profound funnel shaped cavity is 

 observable. 



The basal plate (pelvis) is small and lines about one half of this funnel-shaped 

 cavity, at the apex of which is a small circular impression for the insertion of a 

 column. This pelvis is composed of three pieces, two pentagonal and one 

 trapezoidal. 



Costals five; elongated, equal, extending along the whole height of the body, bent 

 upwards inferiorly to articulate with the pelvic plates in the funnel-shaped cavity. 

 The summit of each plate is obliquely truncated on both sides of the ambulacra, so 

 that when these plates are united together, five reentering angles are formed in 

 which rest the inferior salient angles of the superior plates. A longitudinal medial 

 ridge extends over each plate, and projects a little below its base. These ridges, 

 which are more prominent 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, perforated at the summit by a minute rounded opening. 



It occurs in the sub-carboniferous 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-laborer, Dr. J. G. Norwood, of Madison, Indiana. 



