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, etc. — Restricted to the Hudson Eiver group of America. 



Ty^e of the genus : — Tanaocrinus typus W. and Sp. 



Tanaocrinus typUS (nov. spec), W. and Sp. 

 Plate IX. Figs 7a, h, c. 



A small and slender species. Calyx elongate ; broadly truncate at the 

 lower end ; plates without ornamentation. 



Basals ^yq, 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 wdde 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 w^ell 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 wdde 

 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 



