400 THE CRINOIDEA CAMERATA OF NORTH AMERICA. 
lower faces convex. Second costals pentangular, in width and length resem- 
bling the first. Distichals varying from two to three, owing to the number of 
arms in the specimen; smaller than the costals. When there are four arms 
to each ray, which probably is the normal number, they consist of 2 X 2 
plates, and these are followed by 2X 2 palmars; when, however, which is 
quite frequently the case, the anterior ray has only two arms, it has three 
successive distichals in both divisions. Specimens with three arms in the 
anterior ray are comparatively rare, in this case the one division has three 
distichals, the other two, Palmars short, in contact laterally, and rounded 
like arm plates, leaving longitudinal depressions at their sides. Arm facets 
large, directed outward; the ambulacral openings elongate, almost equidis- 
tant, the interspace between the two posterior rays being a little the widest. 
Respiratory pores large, separated from the ambulacral passages by thin par- 
titions, which frequently are not preserved. Arms eighteen to twenty, stout, 
long, incurving and biserial. The lower portions of the plates are rounded, 
and every third plate of both series is extended to form a short lateral spine; 
the upper portions gradually grow flat, and increase in width to twice that 
at the bottom, but do not attain that sharp knife-like edge observed in some 
species of this genus. Interbrachials from one to three; the first very large 
rising to the top of the first distichals; the upper plates, when present, very 
minute. Anal piece higher than the radials; succeeded by three large plates, 
and these sometimes by one or two small ones. Ventral disk depressed 
hemispherical ; the plates highly convex or nodose. Posterior oral strictly 
central, fully twice as large as any of the other plates, and surmounted by 
a high node. The four other orals and the radial dome plates are consider- 
ably larger and more prominent than the interambulacral pieces, some of 
which are quite small. Anal tube excentric and very slender; its length not 
known. Column near the calyx composed of high joints, angular along their 
edges. 
Forizon and Locahty.— Lower Burlington limestone, Burlington, Iowa, 
and Lake Valley, New Mexico. 
Types in the Museum of Comparative Zodlogy, and in the University 
Museum at Ann Arbor. 
Remarks. — This species was described by Hall as having twenty arms. 
Among twenty-one specimens in our collection, which all undoubtedly be- 
long to it, there are ten with twenty arms; five have nineteen, and six but 
eighteen. The deficiency always occurs in the anterior ray. 
-~ 
SP Part corn Ra mes meee a ere P 
~The corte emcee esti HNONRT Re tT Aa RT ER TRE 2% NR Rea ty ae TRS 
