750 THE CRINOIDEA CAMERATA OF NORTH AMERICA. 
spine. The spines, which bristle upward and outward, are acicular, very | 
long and slender, varying in length from ten to twelve mm., somewhat 
thicker near the proximal end, and slightly pitted at the bottom. Column 
round and comparatively thin. | 
Horizon and Locahty. — Chemung group, Ithaca division; Ithaca, N. Y. 
Types in the collection of Prof. Henry 8. Williams at Cornell University. | 
Ltemarks. — The description was made from natural moulds formed in — 
the rock after disintegration of the calcareous test, and from gutta percha 
casts therefrom. 
Arthracantha punctobrachiata Witt1AMs. : 
Plate LX XVI. Figs. 2a, b. 
1883. Wuitt1ams; Proceed. Amer. Philos. Soc. (April), pp. 83 and 86. 
1885. W.and Sp.; Revision, Paleocr., Part III., p. 119. 
1887. Wuuirtravns; Contr. to Canad. Paleont., Vol. I., p. 98, Plate 18, Figs. 1, la. 
Syn. Platycrinus (2) punctobrachiatus Haut (figured by Hall 1872, in Bull. I. N. Y. State Museum 
Nat. Hist.). 
Syn. Hystricrinus Carpentert HinpE, 1885; Ann. and Mag. Nat. Hist., p. 162, Plate 4. 
- a = te - anes a = = Se ge ee ee at’ 
= ape ee —— = o ——- — > ; Sistine eee > ok om a , — es 
TF peak Si a = = =r en : ————— ee = 2 — = = = ~ = 
_ _ eee en ———————————— a Ce = = — I eee esl te TN 
Dorsal cup obconical ; more rapidly spreading at the basals than at the 
A ae TR 
"a radials; the latter somewhat inflected at the upper ends. Ventral disk 
hemispherical, flattened in the central part. Plates without ornamentation, 
| 
| 
: 
| but thickly covered by minute spine-bearing tubercles, which, when well 
| preserved, resemble small cones truncated at the upper end. The spines 
HD | f are elongate, cylindrical, and measure from fifteen to thirty-five mm. in 
A length; they have a short neck at the proximal end, and taper distally. 
nie | The distribution and arrangement of the tubercles is quite irregular; they 
( a are, as a rule, more numerous upon the basals and radials, but the number 
varies even among corresponding plates of the same individual. There are 
ae but very few upon the distichals and interbrachials, but they are crowded | | 
along the median portions of the disk, where, according to Hinde, they are / 
shorter and comparatively thicker than at the arms. 
| Basals large, almost of uniform size; the suture lines indistinct; the 
iat lower end truncated to the width of the column. Radials somewhat irregular 
By in form, the two facing the anal plate narrower at the lower face than at the 
upper, and narrower throughout, the others almost rectangular, and nearly 
as long as wide. The upper faces are straight, except the median part, 
a which is slightly excavated for the reception of the costals; the outer faces 
