HEXACEINID^. 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 stont, 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. 



Horizon 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. 



Dichoerinus HuntsviUse W. and Sp. (nov. spec). 

 Plate LXXV. Ficj. 4. 



Syn. Flati/erinm parvuhs Meek and Wokthen; 1865, Geol. Rep. Illiuois, 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. Eadials 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. 



