ICHTHYOCRINIDAE 323 



which they can be seen, 41 have three IIBr, 1 has four, and 1 has five. In one exceptional 

 specimen 7 out of 10 rami have four. 



The number of tertibrachs runs from at least 10 to 15 or more, with apparently no 

 further bifurcation ; the arms appear to taper to a rather blunt point, without any indication 

 of such coiling as is observed in the Silurian forms. This extension of the tertibrachs obtains 

 also in M. clarkeiisis and M. tiaraeformis, where the number ranges a little higher, being 

 rarely less than 13, while the contrast with the Silurian forms of the family is very marked, 

 they having usually from 7 to 10 tertibrachs with one or more bifurcations following. In 

 conformity with the slightly more elongate form, the brachials in this species and M. clark- 

 eiisis are proportionally a little longer than in M. tiaraeformis, the height to width being 1 to 

 2.4, as against 1 to 3 in that species. Whether there are any differences in the column cannot 

 be ascertained, as it is only known in this species, where it shows somewhat irregular features 

 in two specimens. The enlargement at the top is not very prominent, indeed in one specimen 

 it seems not to be present at all. 



Although this is the best represented species of the genus, specimens of it are extremely 

 rare, not over a dozen having been found in all the collections made at Burlington. It occurs 

 in the Lower Burlington limestone, and has not been found, beyond a single doubtful frag- 

 ment, in the upper bed of that formation. Fragmentary specimens perhaps of this species 

 have been found in the Fern Glen horizon (Kinderhook) Missouri. 



Type. The specimen used by Hall in his description and which was figured by Whitfield 

 in Mem. American Museum, volume 1, plate 3, figure 24, is in the American Museum, New 

 York. The specimens figured here are in the author's collection. 



Horizon and locality. Lower Carboniferous, Kinderhook and Burlington ; Burlington, 

 Iowa and Fern Glen, Missouri. 



Metichthyocrinus clarkensis (Miller and Gurley) 

 Plate XXXIX, figs. 8-18 



Ichthyocrinus clarkensis Miller and Gurley, Bull. 5, Illinois St. Mus., 1894, p. 43, pi. 4, fig. 5. — Beede, 30th 

 Rep. Geol. and Nat. Hist. Indiana, 1906, p. 1257, pi. 14, fig. 4. 



A large species. Crown elongate ovoid, higher than wide, greatest width 

 about IJIB1-2; height to width at lIBn, i to 1.6; at IAx, i to 2.1 ; spread of calyx 

 from column to IIBn, 1 to 4; to IAx, 1 to 2.7; cross-section circular at IIBr 3 , but 

 above that obtusely decagonal owing to the convexity of the arms and depres- 

 sion of the interbrachial sutures; side outline convex; surface smooth, plates 

 strongly imbricated. Maximum crown, 33 mm. high by 28 mm. wide. 



IBB minute, not over half the diameter of column facet. BB small, visible, 

 if at all, only as small points beyond the column. RR partly resting on column. 

 IBri and corresponding brachial of higher series about 1 to 2.4 in height to 

 width. IIBr generally 4. IIIBr 13 to 17 or more, transversely convex. Arms 

 well rounded, closely abutting, tapering but little before infolding, and without 

 farther visible bifurcation. Column facet indented, including IBB, most or all 

 of BB and part of RR. Column unknown. 



In addition to its larger size, and usually greater number of secundibrachs, this species 

 is distinguished from M. burlingtonensis by the greater roundness of the arms and less deli- 

 cate construction. In that species there is almost no convexity of the plates or depression at 

 the interbrachial sutures, and the sutures throughout are marked by light, delicate lines ; 



