288 S. WELLER FAUNA OF THE FERN GLEN FORMATION 



MESPILOCRINUS sp. 



Plate 11, figure 26 



Several specimens of a tripartite crinoid base in the Fern Glen fauna 

 have been recognized by Springer as the underbasals of a flexible crinoid, 

 probably belonging to the genus Mespilocrinus. This identification is 

 strengthened by the undoubted presence among the crinoid fragments of 

 the peculiar column joints of this genus. 



METICHTHYOCRINUS sp. 



Plate 11, figure 25 



A fragment of a dorsal cup, including the base and the radials, has 

 been recognized by Springer as Metichthyocrinus. This genus has not 

 hitherto been recognized in beds older than the Lower Burlington. 



BLASTDIDEA 

 PENTREMITES DECUSSATUS Shumard 



1857. Pentremites decussatus Shumard, Transactions of the Saint Louis Acad- 

 emy of Science, volume 1, page 242, plate 9, figures 6a-b. 



Plate 11, figures 28-29 



Description. — Body subovate in form, broadest below the middle. 

 Basal plates very small, apparently forming a flat, horizontal disk., 

 Eadial plates very long, their proximal extremities inflected and probably 

 being in nearly the same plane as the basal disk ; the ambulacral sinuses 

 very deep, their lower extremities extending nearly to the edge of the 

 inflected, proximal portion; just below the very base of the sinuses the 

 surface of each radial plate is produced into a low but distinct, pointed 

 tubercle. Deltoid plates distinctly angular below, their height being 

 about two-sevenths of the height of the lateral limbs of the radial plates. 

 Ambulacral sinuses moderately wide, the width increasing toward the 

 summit; the lancet plate entirely covered in the lower portion of the 

 ambulacral area by the side plates, but toward the summit it is possibly 

 exposed to a slight degree ; the side plates are rather large, a little oblique 

 in position, their inner extremities directed distally to a slight degree; 

 those of the two series alternate in position ; the median line of the ambu- 

 lacra marked by a zigzag median furrow; the inner extremities of the 

 side plates have a very narrow, slightly raised border, behind which is a 

 depressed band marked by very fine transverse crenulations. The lateral 

 surfaces of the radial and deltoid plates, from the base of the radial 

 sinuses to their summit, are beautifully marked by fine, transverse costag 



