eee A hs 2, : pe Set : é = b} oe Pee ge RS 2 tS fh" 38 = Lbs << Sal , Ss _ ESS EES Se OP Ee Ss 
: s { oe Ses Ne ee a LT A AA A = 
ee Ss = es = —————— = = amide eat 
HEX ACRINID&. TAT 
Basal cup large, broadly obconical, its height about three eighths the 
length of the calyx to the arms, its lower end slightly projecting and trun- 
cated, the truncated part completely occupied by the large upper stem joint. 
Radials gradually spreading, their upper faces nearly one-third wider than 
the lower, and equal to the length of the plates ; the lower faces in three of 
the plates a little convex, in the two meeting the interbasal sutures slightly 
angular; facets deep, semicircular. The outer surface of the radials is 
marked by a median ridge, rather faint at the lower end, but growing wider 
and quite prominent upward. Costals two, short, twice as wide as long, 
rounded on the back. Of the distichals only two single plates are preserved ; 
they are as wide as, but shorter than, the costals, and are connected laterally. 
All other parts wanting in the two type specimens, with the exception of 
a few joints of the stem, which are round and extremely short. The nodal 
joints are very much the widest, their projecting edges exceedingly thin and 
knife-like ; while the edges of the internodal joints are rounded. 
Horizon and Locality.— Lower part of Hamilton group; Louisville, Ky. 
Type in the collection of the late Major 8. 8, Lyon. 
ARTHRACANTHA Witt1Ams. 
1883. H. 8. Wiit1ams; Proceed. Amer. Philos. Soc. (April), p. 84. 
1885. W.and Sp.; Revision, Paleocr., Part IIT., p. 116 (Proceed. Acad. Nat. Sci. Phila., p. 338). 
1887. Wuuiteaves; Contr. to Canad. Paleont., Vol. L, p. 96. 
1889. S.A. Mitter; N. Amer. Geol. and Paleont., p. 225. 
Syn. Hystricrinus Hinpe; 1885, Ann. and Mag. Nat. Hist., p. 158. 
Plates arranged as in Hevracrinus, but covered with numerous tubercles, | 
each of them having a small pit for the reception of a movable spine. Basals | 
three, large, subequal, and pentangular. Radials and anal plate as in Hemxa- 
crinus. Costals two, comparatively large, and forming part of the dorsal 
cup. JDistichals three to four, small, curved like arm plates and directed 
outward; those of the same ray separated by interaxillaries or in contact 
laterally. Arms branching, biserial ; pinnules of moderate size. 
Interradial plates numerous, covered like the plates of the dorsal cup, 
with irregularly arranged, spine-bearing tubercles. Anal opening excentric. 
Column round. 
Distribution. — Upper Devonian, and only found in the neighborhood of 
Lake Ontario. 
Type of the genus: Arthracantha ithacensis Williams. 
