340 PALAEONTOLOGY OF ILLINOIS. 



tylus and A. polydactylus, and deKouinck's A. stellaris, A. diversus,* 

 A. deornatus and A. armatus, with various others ; and the group includ- 

 ing A. multibrachiatus and its allies. 



The typical forms of Actinocrinites, which agree almost exactly with 

 all the other genera mentioned, as well as with the A. multibrachiatus 

 group, in the number and arrangement of the pieces composing the 

 walls of the body below the bifurcations of the rays, are distinguished 

 by the following characters, never found all combined in any one of the 

 other groups : 



In the first place, they have the arm bases, or brachial pieces, and 

 adjacent parts (sometimes as far in as the third primary radials) grouped 

 together so as to form five more or less protuberant lobes,* and so far 

 as yet known to us, at least a part of the arms bifurcating after becom- 

 ing free, and always each composed of a single series of pieces below 

 each bifurcation, as well as generally for some little distance above. 

 They also combine with these characters a more or less produced cen- 

 tral or sub-central tube or proboscis, and have the second primary radial 

 pieces nearly always normally hexagonal. 



The other group represented by A. multibrachiatus differs from the 

 typical forms of Actinocrinites in having the arm bases arranged in a 

 nearly or quite continuous series all around, and the arms never bifurca- 

 ting after becoming free, as well as in nearly always having normally 

 the same number of arms in each ray. The species of this group also 

 more generally have the vault higher in proportion to the body below 

 the arms, but there are a few exceptions to this in both groups. In a 

 few species of typical Actinocrinites the arm bases are less distinctly 

 grouped, and not so protuberant as in others, but so far as we have yet 

 seen they can readily be distinguised by the structure and bifurcations 

 of their arms, where specimens retaining them can be seen, and nearly 

 always, even where the arms are broken away, by their wider inter- 

 radial and anal sinuses and other peculiarities of general physiognomy, 

 apparent enough to the eye but difficult to express in words. 



In having the arm bases arranged in a nearly or quite continuous 

 series all around, and the arms never bifurcating after becoming free, 

 tue A. multibrachiatus group agrees with Batocrinus, but it differs from 

 that group in having longer arms in proportion to the length of the pro- 

 boscis, which in Batocrinus, when entire, protrudes from one-fourth to 



*Since these remarks were in type, we observe, on consulting Miller's Nat. Hist, of the Crinoid-ea, 

 to which we had not previously had access for many years past, that he seems to have confounded two 

 very distinct forms under the one name of his typical species, Actinocrinites triacontadactylus. One of 

 these, if correctly represented on Plate I of his work, must belong to an entirely different species from 

 that figured under the same name on his Plate II, as it is represented as having its arm bases and 

 contiguous parts, not forming five widely separated protuberant lobes, but arranged more like those in 

 the American section represented by such forms as A. mvMibrachiatus, though its arms clearly bifur- 

 cate after becoming free. 



