66 OWEN AND SHUMARD'S FOSSIL CRINOIDEA. 



It occurs in the sub-carboniferous 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. " 



Diameter of pelvis, - - - 



1.6 « 



Length of perisomic plates, 



6. " 



Width of " u . . 



3. " 



Pentremites laterniformis. (New sp.) 

 Fiff. 15. 



o 



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. 



It presents somewhat the appearance of a street lamp, its lower portion having the 

 form of a truncated pentagonal pyramid inverted, while its upper part is dome- 

 shaped. 



The hasal plate is composed of three pieces, two are widened pentagons, and one 

 is a rhomb ; united together they form an irregular octagon with three obtuse 

 re-entering angles, to the points of which the basal sutures radiate. 



Perisomic plates five, elongated ; their length being to their breadth about as one 

 to two ; three of them terminate inferiorly in an obtuse salient angle, each angle 

 corresponding to one of the retreating angles formed by the union of the basal 

 pieces, two terminate below in a straight edge and rest on the superior margins of 

 the pentagonal basals. A triangular fold projects exteriorly from the superior 

 portion of each plate. The apex of this triangle points downwards and extends 

 nearly to the middle of the plate. These folds are notched superiorly for the 

 reception of the five radiating ambulacra, and a portion of the superior plates, and on 

 either side is a short straight edge. 



The superior plates are dart-shaped, the barbs being inserted into the triangular 

 notch on either side of the ambulacra, while the intervening edges rest on the 

 corresponding straight margins of the perisomic plates included between the folds. 

 The point of the dart terminates at the apex of the fossil. The ambulacra widen 

 slightly from below upwards. 



This Pentremite was obtained from the carboniferous strata on Mill Creek, 

 Randolph county, Illinois, about seven miles from Chester. 



