718 THE CRINOIDEA CAMERATA OF NORTH AMERICA. 
The latter curve outward to the costals, and meet the covering pieces. 
. ‘When there are more than three plates, the upper ones are very small. 
: Anus placed between the two posterior orals, the opening directed laterally. 
| Horizon and Locality.— Lower Burlington limestone; Burlington, Iowa, 
| 
. 
| 
TN 
and Lake Valley, New Mexico. 
Type in the (Worthen) Illinois State collection (a rather poor specimen). 
wins — aay 
fiemarks.— In a very fine specimen, evidently of this species, Plate | 
LXVI., Fig. 9a, there is an indistinct node within the five angles of the basal | 
disk, and three others, even more obscure, upon the beveled edges at the 
GLE IG ET RL GR 
lower end of the radials. 
Platycrinus excavatus Hatt. 
Plate LXVI, Fig. 4. 
1861. Hains Descr. New Species Crin., p. 4; also Boston Journ. Nat. Hist., Vol. VIL, p. 286 (figured 
1872 N. Y. State Mus. Nat. Hist., Bull. I., Plate 2.4, Fig. 1). 
| 1893 Wuuitrierp; Mem. Am. Mus. Nat. Hist., Vol. L, Part I., p. 8, Plate IIT., Fig. 5. 
i Ly Syn. Platycrinus sulcatus MitLER, 1891; Geol. Surv. Missouri, Bull. 4, p. 16, Plate 2, Fig. 2. 
Wa | A rather robust species, not above medium size. Dorsal cup discoid, 
iq | forming a flat basin. Only the extreme outer margin of the basal disk 
| projecting below the margin of the radials, the inner portions deeply de- 
HH) \ ° e e e j 
It | pressed so as to embrace the three or four proximal stem joints, which do | 
Hy : ° : 
ie | not, however, touch the sides of the concavity. The radials expand very , 
Ht , rapidly, curving but little; their upper faces twice as wide as the lower ones; | 
the facets subcircular, somewhat concave, and directed outward and slightly 
downward. Interbasal sutures obscure, the basi-radial and interradial ones 
Waid profoundly and widely channeled; the sides of the basal disk and radials 
| 2 beveled. Outer margins of radials surrounded by a thickened rim or rugose 
| swelling, and the facets by a slight ridge, producing a rather abrupt depres- 
triangular, frequently not occupying the full width of the facet; the distichals 
then touching the radials, and their sloping upper faces making a right : 
i sion in the median portions of the plates. Surface of basals smooth. Costals 
| 
. i/ | angle. Distichals two; the lower one twice as wide as long; the upper 
ly wider than the lower, the upper angle obtuse. Arms four to the ray, very 
| fi I | stout and short, slightly tapering at the tips. Structure of the ventral disk 
| ut | unknown, except that the anus was at the end of a tube which extended to 
| | the full height of the arms, and was composed of spiniform plates. . | 
| f ij | Horizon and Locality. — Lower Burlington limestone, Burlington, Iowa. 
t ] 1 
2 Fe 
a Pirncsiareey tt 
