154 PROCEEDINGS OF THE ACADEMY OF 



least a part of the arms bifurcating after becoming free, and always each com- 

 posed 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 central or subcentral tube or proboscis, and have the 

 second primary radial pieces nearly always normally hexagonal. 



The other group represented by A. multihrachiaius 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 wfrer bifurcating tf/"if«r 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 Actinocriles 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 distinguished by the structure and bifurca- 

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

 always, even where the arms are broken away, by their wider interradial 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, the A. muUihra- 

 chiatus group agrees with Bafocrinun, but it differs from that group in having 

 longer arms in proportion to the length of the proboscis, which in Batocrinus, 

 when entire, protrudes from one-fourth to one-half its entire length beyond the 

 extreme length of the arms.* They also difter from Balocrinus and agree with 

 Actinocrinites in nearly always (perha[)S always normally) having the second 

 radial pieces hexagonal instead of quadrangular, while their body plates are 

 more or less sculptured (generally strongly so) into radiating costre, usually 

 consisting of a single rib for each side of each plate, instead of having the 

 plates even and smooth, merely convex or tumid. In short, the species of these 

 two groups can be distinguished at a glance from specimens even showing the 

 body only.f 



As thus limited, the genus Actinocrinites would include, along with a number 

 of foreign species, the following American Carboniferous forms :J 



1. Actinocrinites, Miller. Section (a). 



A. verrucosus {= A. asterius, McC), A. chloris (= A. ienuisculptus, McC), A. 

 lobatus, A. Ilumboldtianus, A. jugosus, A. pernodosus, A. unicostalus, A. Loivei, 

 A. hrojitcs, &c., cff Hall. Also, A. Yandelli and A. multiradiatus, Shumard ; A. 

 Wachsmtithi^ White; and A. scitulus, M. and W. (= A. riisticus, Hall, and ^4. 

 Sillimani, M. and W.); as well as our A. penicillus and A. delicatus, of this 

 paper, and A. Jndianensis, L. and C, with perhaps several others with which 

 we are not very well acquainted.^ 



2. Section (b). 



A. multibrachiatus, A. proboscidialis,\\ A. cselatus, A. clavus, A. limibrachiatus, 



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. multil>racltiutus, though its arms clearly bifurcate after 

 becoming tree. 



* See figs. 1 and 2, pi. 11, Iowa Geo'l Report, vol. 1, pt. ii. 



f See pi. X, fig. 10, Iowa Geol. Report, vol. 1, pt. ii. For other examples of this group see 

 figs. 13 & 14 same plate, where they may be compared with figs. 7 & 9 of the same plate, 

 representing two species of true Actinocrinus, with arm bases grouped into 5 protuberant 

 lobes. 



J There are ^ome other described .American species not mentioned in this list, which is 

 only intended to include such species as we have had an opportunity to study. 



^ t)r. Shumard's A. concimis belongs here, if not a Stfganocriniis. We have not yet seen a 

 specimen of it showing the rays far enough out to decide positively to which of these 

 groups it belongs. 



Ij A. quatemartus, A. quaternarius var. spiniferus and A. Themis. HM, are believed to be va- 

 rieties of his A. proboscidians. 



[July, 



