PLATYCEIKID^. 679 



between the five or six proximal plates of the arms. Distichals two, directed 

 Tipwards, rather large, the first nearly once and a half as wide as long, and 

 pinnule-bearing ; the second a little longer and axillary ; their upper angles 

 acute. The distichals generally support a single arm on either side ; occa- 

 sionally, however, one of the plates — or both of them — gives off an arm 

 from its outer side, and two palmars with two arms from the inner one. The 

 two palmars, when represented, are as large as the distichals, but proportion- 

 ally higher. Arms free above the first distichals, from four to six to the ray, 

 the number often varying in the same specimen ; rather heavy, especially 

 at midway, where in adult specimens they are often twice, and even three 

 times, as thick as near the calyx. They are biserial at the upper end, uni- 

 serial to the fifth or sixth joint ; the latter plates, which are moderately long 

 and wedge-formed, are alternately arranged and gradually interlock. The 

 distichals and the cuneate arm pieces are constricted in the middle, and pro- 

 vided laterally with sharp, thorn-like projections at their upper and lower 

 ends, which sometimes extend to the biserial portions of the arms. Pin- 

 nules stout, long, closely packed, and composed of long joints ; the one from 

 the first distichal stouter than the rest, and less erect. Of the ventral disk 

 only the middle plate of the interambulacral series has been observed ; it is 

 visible in a side view, and crowned by a small tubercle or short spine. Stem 

 joints elliptical and moderately long; the nodal ones at the lower part of the 

 stem quite prominent, and their margins in well preserved specimens sur- 

 rounded by bead-like nodes or short thorns. 



Horizon and Locality. — St Louis limestone, Huntsville, Ala., and Hardin 

 Co., 111. At Huntsville it is found about sixty feet below the Pentremites 

 Godoni beds, where it occurs in small pockets in large numbers. 



Types in the collection of Wachsmuth and Springer. 



Remarks. — The name Platycrinus Huntsvillce appears in Troost's List of 

 the Crinoidea of Tennessee, published in the Proceedings of the American 

 Association for the Advancement of Science, Cambridge meeting, 1849, with- 

 out figure or description, and has ever since been applied by palaeontologists 

 and collectors to the only form of Platycrinus occurring near Huntsville. 

 We are aware that this does not establish Troost's name. 



In 1860, Meek and "Worthen described as P. penicillus and P. plcmis two 

 specimens from Hardin Co., 111., both of which we have examined, and which 

 we have reason to regard as aberrant forms of P. HunisvillcB. Looking at 

 the two specimens alone, one would say at first sight that they are distinct 



