438 THE CRINOIDEA CAMERATA OF NORTH AMERICA. 
of the costals — whence it spreads abruptly to the arm bases. Plates heavy, 
their>middle portions generally prominent, their surfaces smooth, and the 
suture lines not impressed. | 
Base once and a half as wide as long, truncated at the bottom, and slightly 
spreading outward from the lower edge; column facet deeply impressed. 
Radials large, generally longer than wide, often decidedly so; rising verti- 
cally. Costals small ; the first quadrangular, not more than one fourth the 
size of the radials; the second a little wider but not longer than the first. 
Distichals 2 x 10, of the same size as the costals. Each one is followed by 
two palmars, which either form a continuous series around the calyx, or are 
separated between the rays by a small interdistichal plate. Arm bases pro- 
jecting ; the arm openings directed obliquely upwards. Arms four to the 
ray, short, rather flat and heavy. They are composed of two rows of short / 
pieces alternately arranged, which are produced laterally into slender, sharply 
a pointed spines extending out from the sides of the arms. Interbrachial plates 
iene | 1, 2, 2, followed sometimes by another narrow plate. Anal plate as large 
as the radials ; supporting three smaller plates in the first range, and three 
in the second, which are frequently followed by one or two other plates. 
| li Tegmen conical, slightly bulging ; composed of large convex or nodose 
WET pieces, which are continued to the anal tube. Orals excentric, and a little 
| larger than the surrounding plates, especially the posterior one. The radial 
dome plates are also readily distinguished by their larger size and greater ” 
convexity. Anal tube almost central, very long and heavy, often rising to 
Pt) three times the length of the arms ; it gradually tapers, and has at the upper 
Lie end a minute opening. Column long, rather stout. It has been observed to 
‘ the length of twenty inches, to which it neither increases nor decreases 
in size, and the length of the joints remains unaltered; but the edges of 
| 
i the upper ones are slightly convex, while the lower joints are strictly 
| cylindrical. : 
iF Fforizon and Locality. — One of the leading fossils of the Upper Burling- 
i \/ ton limestone, and found wherever that is exposed throughout Iowa, Illinois, 
it and Missouri. 
lies Remarks. — A. pyriformis, var. rudis, is in our opinion identical with this 
species. The original specimen was said to come from the Kinderhook group 
of Marion Co., Ills.; but we doubt it, for it is a true Upper Burlington type. 
