190 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. xxxvi. 



ing more or less to project downward over the proximal column joints, 

 as in most recent sjiecies. 



The bifurcation of the arms so far beyond the axillary IBr is an 

 unusual feature, occurring in the largest specimen at the twenty- 

 seventh to the thirtieth brachial (Plate 4, fig. 1), and in other 

 specimens from the sixteenth to the twenty-third. I know of no 

 Pentacrinoid in which arm division takes place so high up ; nor in 

 fact any inadunate crinoid, the nearest approach to it being found 

 in the Carboniferous genus Poteriocrinus. There is little tendency 

 of the arms to spread out, but they are long and slender, tending 

 rather to lie in a bundle. The general aspect of calyx and arms is 

 somewhat like that of /. na7'esiamis, which it also resembles in the 

 number and regularity of the syzygies, which is unusual in the Penta- 

 crinida\ I can trace them in two arms of specimen A (Plate 4, 

 tig. 1) part way, and in one to the end, and can distinguish them in 

 the- distal portion of some other arms. Beginning at IIBr 3-(-4, they 

 occur at intervals of mostly about 10 brachials, but sometimes 4, 5, 

 or 6. I give a figure of the pair next to the last, being about brachials 

 79+80 of that arm. (Plate 4, fig. la.) 



The type-specimens figured are deposited in the U. S. National 

 Museum, where they will be available for comparison with the mag- 

 nificent collection of recent crinoids now being accumulated there. 

 For convenience of reference they are designated by the letters, A, By 

 etc., as indicated in the explanation of the plate. 



EXPLANATION OF IT.ATE 4. 



Isocriiius liiiiiliti, new species. 



Fig. 1. Large specimen. A; witli bifurcating amis complete and part of stem; 

 cirri mostly lost. 

 la. Syz.vg.y at 1 1 IBr Tl)+80 of same specimen. 



2. Large specimen, B; witli stem 140 mm., and jiart of arms. Some arms 



of another individual attached. 

 2a. Detail of stem at "«" of same specimen, showing interarticular 



pores, X2. 

 2b. Detail of same at " h;"' showing cirrus soclcets, X2. 



3. Small specimen, C; with part of arms, some not bifurcating. 



3a. Calyx and lower IIIBr of same specimen; showing form and pro]K)r- 

 tions of basal and radial plates, X2. 



4. Small specimen, D ; with part of arms, one with an axillary, and some 



apparently simple. 



5. Small specimen, E; with two arms simple and one bifurcating at 2.3d 



IIIBr; stem detached, exposing infrabasals. 



5a. Basal view of same specimen, showing infrabasals, X4. 



6-8. Portions of different stems, F, G, H ; showing cirri. 



7a. The longest cirrus on specimen G, X2. 



9-13. Weathered stem joints associated with the other specimens; 9, 10, 11 

 are mature internodals; 12 is the proximal face of a nodal incised 

 by the cirrus sockets ; 13 is a deeply stellate joint from the young- 

 est part of the stem; all, X2, 



