NATURAL SCIENCES OF PHILADELPHIA. 13l 



lose, and we have not been able to see any indications of the small patelloid 

 pieces between the radial and arm pieces as in F. exscu'ptus. 



Locality and position. River Bluff, near the south line of Monroe County, 

 Illinois. Keokuk Limestone of the Lower Carboniferous series. 



Forbesiocrinus Agassizi, var. giganteus. This large Crinoid differs from the 

 typical specimen of F. Agassizi (Hall), in having four instead of three plates 

 in each secondary ray ; (in three of the rays seen) while there are some differ- 

 ences in the number and arrangement of the anal and interradial plates. It 

 also differs in having its column almost exactly cylindrical for a distance of at 

 least four inches below the base, while that of F. Agassizi, is described as 

 "rapidly tapering below the summit." We suspect it may prove to be a dis- 

 tinct species from that described by Prof. Hall, but as it agrees with his des- 

 cription and diagram in most of its characters, excepting the points of differ- 

 ence we have mentioned, we merely call attention to it as a variety of that 

 species, until we can have an opportunity to compare better examples of it 

 with authentic specimens or figures of Prof. Hall's species. Should it prove 

 to be distinct, it can take the name giganteus, which would be very appropri- 

 ate, since it is the largest species of that genus known, the length of its body 

 to the commencement of its free arms being near 3 -30 inches, and its breadth 

 apparently about the same. Its arms are proportionally short, and bifurcate 

 frequently. 



Locality and position. Burlington, Iowa. Burlington Limestone. 



Genus ACTINOCRINUS, Miller, 1821. 



Actinocrinus dodecadactylus. Body rather small, subglobose ; summit and 

 calyx below the arms of nearly the same size ; breadth a little greater than 

 the- height ; composed of slightly convex, smooth or subgranulose plates, 

 which are connected by moderately distinct sutures. Base small, much de- 

 pressed or subdiscoidal, obtusely hexagonal in outline, with three other obtuse 

 retreating angles at the sutures. First radial plates wider than long, three 

 of them regularly hexagonal, and two heptagonal. Second radial pieces much 

 smaller than the first, about twice as wide as long, and all quadrangular. 

 Third radials a little larger than the second, all regularly hexagonal, the two 

 lateral margins being very short, and the two superior sides each about 

 equalling the base. In the two posterior rays, the third radial pieces each 

 support on one of their superior sloping sides a large brachial piece, and on 

 the other a secondary radial of near the same size, which, in its turn, supports 

 two brachial pieces, making three arms to each of these rays ; while in all the 

 others, two brachial pieces rest directly upon the third radial, thus making 

 only twelve arms in the whole series. The first anal plate is about as wide as 

 the first radials, but a little longer, being longer than wide, instead of the re- 

 verse. It is regularly heptagonal, and supports on each superior lateral slop- 

 ing side, a smaller heptagonal piece ; while an elongated, coffin-shaped piece 

 rests upon its short superior truncated side, between the two latter, and ex- 

 tends up, flanked on either side by the first brachials, to its connection with 

 the summit. Each of the interradial spaces is filled by a single ovate, octago- 

 nal piece, about as large as the second and third radial pieces taken together. 



The vault is composed of rather large, somewhat regularly arranged plates 

 which are very nearly flat, the smaller ones all being on the anal side ; the 

 proboscis is small, and located nearer the anal than the dorsal side. 



Height to base of proboscis, 0-50 inch; breadth, - 58 inch; breadth of base, 

 0-23 inch. 



Locality and position. Burlington, Iowa. Burlington Limestone. 



Actinocrinus ptriformis, var. rudis. Actinocrinus pyriformis, Shumard, 1855, 

 Geol. Report of Missouri, p. 192, pi. A, fig. 6, a, b. 



Body exclusive of the proboscis piriform, being very narrow and apparently 



1861.] 



