186 THE CRINOIDEA CAMERATA OF NORTH AMERICA. 
like arm plates. Distichals numerous, for the most part incorporated into 
the calyx. Arms branching once or twice beyond the calyx. 
Interradial and interdistichal areas deeply depressed, filled by numerous 
minute, irregular pieces. Anal side wider than the other four, divided by 
a median longitudinal row of large anal plates, folded like the costals. 
Structure of the disk and position of the anus unknown. Column round 
or obscurely pentagonal. 
Distribution, ete. — Restricted to the Hudson River group of America. 
Type of the genus: — Tanaocrinus typus W. and Sp. 
Tanaocrinus typus (nov. spec.), W. and Sp. 
Plate IX. Figs 7a, 6, ¢. 
A small and slender species. Calyx elongate; broadly truncate at the 
lower end; plates without ornamentation. 
Basals five, plainly visible in a side view ; forming a short cup, which is 
slightly excavated at the bottom. The upper faces in four of the plates sharply 
angular, that of the posterior side narrowly truncate. Radials the largest 
plates of the calyx, much narrower at the top than at the bottom, rounded 
at the lower face. They are connected laterally, forming a wide and deep 
notch for the reception of the interradials, except at the anal side where the 
first anal plate rests directly upon the basals. Costals two, as long as the 
radials but narrower; folded and elevated in the middle, the lateral margins 
on a level with the interradials. Distichals seven to eight; all, or nearly 
all of them, incorporated into the calyx; the lower ones as long as the costals, 
but a little narrower; the upper ones gradually growing shorter, and taking 
the form of free arm joints. Palmars twelve or more, all of them free. The 
arms branch two or three times; they are long, cylindrical, and taper gradu- 
ally to the tips, where they become very delicate and thread-like. They are 
composed of short, cuneate pieces which do not interlock. The first pinnule 
is given off from the second distichal ; it is more than twice as large as any 
of the others, and it, as well as the three or four succeeding ones, is enclosed 
in the calyx. Interradial and interdistichal spaces deeply depressed, the 
plates very small and without definite arrangement. Anal side twice as wide 
as the other four, and divided longitudinally by an anal ridge of five to six 
large plates, which closely resemble the radials and costals. The first anal 
plate, which rests upon the basals, is nearly as large as the radials, and like 
