424 SMITHSONIAN INSTITUTION 



forming distinct rounded branches. Near the outer base of each branch a 

 small ramule is given off from the short outer sloping face of axillary IIBr 3 . 

 The main branch continues from the longer, inner sloping face of the axillary, 

 and a similar ramule is given off from the inner side of IIIBr 3 ; another on the 

 outside on about the third brachial ; and so on alternately to a total of 4 or 5 

 ramules (in mature specimens, fewer in young), ending in an equal bifurca- 

 tion ; the last two or three divisions are without much divergence. Each 

 ramule bifurcates on the second or third plate, and again once or twice with 

 short intervals, producing five or more ultimate arms to the ramule; these 

 are rounded and short, forming clusters at the extremities of the main rami 

 where they curve toward the ventral side and fold together in bunches like 

 the fingers of a clenched fist. Brachials in the ramules, as well as main rami 

 above IIBr, short and wide, and usually with arcuate sutures. All brachials 

 from the first primary on becoming free are very deeply rounded, with a deep 

 ventral furrow ramifying into the ramules. iBr in 3 or 4 ranges extending 

 to second or third IBr. Anal tube apparently small, not preserved above first 

 plate in any of the specimens, which shows that it was fragile and bordered by 

 weak perisome. Column of moderate size; the enlargement at calyx slight, 

 tapering gradually downward and passing" into alternating, rather short 

 columnals, which in mature specimens are more or less convex, the longer 

 ones projecting above the others. 



Dimensions of average large specimens, such as the type, figure 1 : length 

 of ray from IBB to top of angle of divergence — that is, the ray below the 

 fork — 35 mm. ; of rami above the fork measured to axil of terminal bifurca- 

 tion, 20 mm. ; diameter of calyx, 30 mm. ; of base at column facet, 8 mm. 1 



This species is typical of what may be called the extreme form of the genus, having 

 widely distended free rays, and a considerable number of iBr plates curving inward over 

 the margins, accompanied by a frequent complete horizontal extension of the whole crown. 

 In this respect the description would apply as well to several species, which might be taken 

 with it to form a fairly distinct group within this genus, viz., O. asteriaeformis, 0. ulrichi 

 and 0. exsculptus. Meek and Worthen in discussing the reasons for separating the species 

 from Forbesiocrinus (Geol. Surv. Illinois, vol. 2, p. 242) gave the following excellent 

 picture of it : 



If we could open and spread out the rays of a Forbesiocrinus upon a plane as far in as to the second 

 radial pieces, and then divide each of the interradial series of plates and fold them up so as to cover the 

 vault, and apparently to some extent the free rays, somewhat in the manner suggested by Prof. Agassiz 

 for the ideal conversion of an Echinoid into a Starfish, we would have a form very like the extreme 

 Onychocrinus. 



The ramules are in strong clusters of 5 or 6 fairly stout finial branches, but the clusters 

 are few in number, not exceeding five counting the terminal one, and usually not so many. 

 Also the clusters diminish in size distally ; while the lowest may have 5 or 6 branches, those 

 above that have progressively fewer, until the last equal bifurcation has two finials to each 

 branch. 



1 The same measurements will be made for all the species. 



