72 



BULLETIN 64, UNITED STATES NATIONAL MUSEUM. 



Genus DIZYGOCRINUS Waehsmuth and Springer. 



DIZYGOCRINUS SACCULUS (Miller and Gurley). 



Plate 5, figs. 1, 2, 3, 4, 5, 6. 



Actinocrinites fibula Troost, Proc. Amer. Ass. Adv. Sci., II (read 1849), 1850, p. 



60 (nomen nudum); MSS., 1850. 

 Actinocrinus fibula Shumard, Trans. Acad. Sci. St. Louis, II, No. 2, 1866, p. 344 



(catalogue name). — Wachsmuth and Springer, Rev. Palseocrinoidea, II, 



1881, p. 224 (catalogue name). 

 Batocrinus sacculus Miller and Gurley, Bull. No. 5, Illinois State Mus. Nat. 



Hist., 1894, p. 52, pi. v, figs. 7, 8, 9.— Weller, Bull. No. 153, U. S. Geol. Surv., 



1898, p. 133 (catalogue name). 



The following description is by Troost: 



This species differs much in its general appearance from the generality of the Actino- 

 crinites, and though the number and arrangement of the plates, which are somewhat 

 obscure in my specimens, seem to be identical with those of the genus Actinocrinites, it 

 is nevertheless with hesitation that I place it in this genus. 



The whole body has the form of a flat circular dish, slightly elevated at the rim and 

 more or less depressed toward the centre. .In the very centre is an elevated ring which 

 seems to have been the first joint of the column having a circular alimentary canal 

 [lumen]. It has twenty [eighteen] horseshoe form apertures for fingers [arms] on the 

 margin of the elevated rim, and a low coronal integument composed of polygonal 

 tumous plates, terminating at the apex in a proboscis so that in this species the viscera 

 were not inclosed in the cavity of a cup but they lay upon an almost flat dish and were 

 covered by a low conical coronal integument. 



They occur near White's Creek Springs. They are rather rare. I found only two 

 specimens — having the form of a button has induced me to give it the name of fibula. 



I consider the fossil represented by figs. [4, 5, 6] as an internal cast of the A. fibula. 

 Breaking a siliceous rock of the Devonian strata, I found it uninjured in a small cavity 

 which has the intaglio form of the fossil. The joints of the plates are at some parts very 

 plain. Below each plate is a depression in which are, from two to four longitudinal 

 apertures. The pelvis [base] is hexagonal and supports two series of hexagonal costals 

 [radials] upon which follows a pentagonal scapular, [primaxil] the joints of the inter- 

 mediate plates are not plain — the rim is surrounded by ten [nine] pair of fingers [arms]. 

 The superior part is compressed hemispherical. From each pair of fingers proceeds 

 a vessel (in bas-relief). These vessels, casts of ambulacra, after ascending a short 

 distance join two and two forming then five large vessels which near the apex join 

 all together and probably communicated in the proboscis — if such organ existed — I 

 see no traces of it on the cast, — but if it really is a cast of the A. fibula, a proboscis 

 must have existed. A little below the apex just hi the angle formed by the junction 

 of two of the five vessels is an elevation which indicates an aperture in the cover, — or 

 may have opened into the proboscis as no trace of an aperture is perceptible near the 

 proboscis in the perfect specimens. 



This was discovered in Stewart County, Tennessee. 



Observations. — Four specimens in the Troost collection agree with 

 Dizygocrinus sacculus (Miller and Gurley) except in the more 

 depressed calyx, but the height of the calyx varies in the four speci- 

 mens at hand and the low cup is, in part at least, due to compression 

 during fossilization. 



These specimens agree in general form with D. decoris Miller, but 

 differ in the entire absence of the strong angular ridges which, in the 

 latter species, cross the radial series of plates from the basals to the 



