HEXACRINID &. 773 
greatest width, the sides straight, the facet for the reception of the costals 
narrow and but slightly excavated. Costals two, apparently followed by 
a single distichal, no line of division being visible in the specimen. Arms 
four to the ray; of medium length, rather strong, and composed of long, 
cuneate plates, which slightly interlock. Pinnules stout, long, and not in 
contact. Anal plate narrower than the radials, but longer and rather dis- 
tinctly angular at the lower end. Structure of the ventral disk unknown. 
Plates of the calyx without ornamentation. 
fTorizon and Locality. — Upper part of Keokuk group; Hamilton, Ills. 
Remarks. — Professor Worthen described this species as having probably 
two arms to the ray, which is certainly incorrect. It is clearly shown from 
the type specimen in the collection of Mr. Lisbon A. Cox, which we have 
figured, that it has four arms, and but two costals followed by a distichal, 
instead of three costals, as he supposed. 
Dichocrinus Huntsville W. and Sp. (nov. spec.). 
Plate LXXV. Fig. 4. 
Syn. Platycrinus parvulus Meex and WortHen; 1865, Geol. Rep. Illinois, Vol. V., p. 555, Plate 20, 
Fig. 7. 
Of very small size. Dorsal cup gradually spreading to the top of the 
basals, the sides along the radials almost parallel. Plates delicate and per- 
fectly smooth, the suture lines indistinct. Basals forming an obconical cup, 
of which the height is equal to two fifths the length of the calyx to the arm 
bases, Radials twice as long as wide; the two posterior ones considerably 
wider above than below, the sides of the three anterior ones almost parallel ; 
the upper faces nearly straight, their median portions but slightly excavated, 
and the sides but little sloping. The anal plate narrower at the top than the 
radials, but wider at the lower end. Costals two, more than twice as wide 
as long and about half the width of the radials; the upper faces of the axil- 
lary somewhat concave. Distichals two, frequently as large as the costals, 
the first sometimes a little narrower: Arms four to the ray, small, rounded 
on the back. They are composed of a few transverse single pieces, followed 
by cuneate ones, which gradually interlock, but the smaller ends do not 
reach the sides of the arm. Pinnules long and stout. Structure of ventral 
disk not known. 
Horizon and Locality.—St. Louis group ; Huntsville and Whitesburg, Ala. 
Types in the collection of Wachsmuth and Springer. 
