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800 THE. CRINOIDEA CAMERATA OF NORTH AMERICA. 
basals. The costals very minute, sometimes completely covered by the dis- 
tichals, which are a little larger than the palmars. The latter, to the height 
of the third plate, consist of short, transverse, single pieces, the plates of the 
two lower rows being included in the calyx; while those of the third row, 
which are surmounted on the back by a small spine or elongate node, are 
free. Arms biserial from the fourth plate, and composed of two rows of very 
short pieces, which are united laterally by a zigzag suture. "The arms are flat, 
tapering, and so short that their ends do not meet upon the summit. Ven- 
tral disk pyramidal, a little shorter than wide. Interambulacral spaces trian- 
gular, and to their full height covered with small longitudinal grooves in 
which the arms rest. At the four regular sides there are four plates, three 
of them interambulacral, arranged: 1 and 2, followed by an oral plate. The 
two upper interambulacral pieces and the orals are strongly bevelled at one 
side to form the sockets for the appendages. The upper parts of the four 
smaller orals bend abruptly inward, and form a sort of platform, which is 
almost invariably occupied by a specimen of Platyceras chesterense, so as to 
cover the anal opening and the posterior oral. Anal interradius a little the 
widest, and composed of a much larger number of plates. It has also only 
one plate between the arm bases, but this is followed by three or four pieces, 
and numerous others which gradually decrease in size upwards. The pos- 
terior oral is convex and semilunate, one of its sides being excavated by the 
anal opening, which is almost central. The sockets for the appendages are 
widest at the top, whence they taper gradually downward, and form a sharp 
angle which enters the upper end of the interdistichal below. The appen- 
dages are long and somewhat variable in form; as a rule, they are wider on 
top than at the bottom, a little deeper than wide, deepest at the proximal 
ends, and they terminate either in a sharp point or a transverse edge. 
Column small and round. 
Horizon and Locality.— Kaskaskia group; Sloans Valley, Pulaski Co., Ky. 
Types n the collection of Professor Wetherby. 
ftemarks. — We regard Pterotocrinus spatulatus Wetherby as. identical 
with the above species. The two were said to differ in the form of their 
appendages, the one being awlshaped at the distal end, the other more 
spatulate. Comparing the figures of the type specimens, the difference is 
very slight, and a comparison of a large number of spines collected from the 
dumps of the Sloans Valley tunnel shows conclusively that there are within 
the limits of this species even greater variations than those referred to. 
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