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 Localiti/. — Lower Bui'lington limestone; Burlington, Iowa, 

 and Lake Valley, New Mexico. 



Type in the (Worthen) Illinois State collection (a rather poor specimen). 



Remarlcs. — In a very fine specimen, evidently of this species, Plate 

 LXVL, 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 

 lower end of the radials. 



Platycrinus excavatus Hall. 

 Plate LXVL Fig. 4. 



1861. Hall J Descr. New Species Crin,, p. 4; ako Boston Jouni. Nat. Hist., Vol. TIT., p. 286 (Bgured 



1872 N. ¥. State Mus. Nat. Hist., BuU. I., Plate 2J, Fig. 1). 

 1893 Whitfield ; Mem. Am. Mus. Nat. Hist., Vol. I., Part 1., p. 3, Plate IH., Fig. 5. 



S.yn. Plati/crimis stdcatus MiLLEK, 1891 ; Geol. Surv. Missouri, BuU. 4, p. 16, Plate 2, Fig. 2. 



A rather robust species, not above medium size. Dorsal cup discoid, 

 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- 

 pressed so as to embrace the three or four proximal stem joints, which do 

 not, however, touch the sides of the concavity. The radials expand very 

 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 

 profoundly and widely channeled ; the sides of the basal disk and radials 

 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- 

 sion in the median portions of the plates. Siirface of basals smooth. Costals 

 triangular, frequently not occupying the full width of the facet ; the distichals 

 then touching the radials, and their sloping upper faces making a right 

 angle. Distichals two ; the lower one twice as wide as long ; the upper 

 wider than the lower, the upper angle obtuse. Arms four to the ray, very 

 stout and short, slightly tapering at the tips. Structure of the ventral disk 

 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. 



Eorizon and Locality. — Lower Burlington limestone, Burlington, Iowa. 



