BATOCRINID^. 465 



lary distichal, which in turn gives off two palmars, one to each side ; while 

 in the antero-lateral rays only the face toward the posterior rays bears an 

 axillary, the opposite face two distichals, which are frequently anchylosed so 

 as to form one large piece. The distichals and palmars are rounded off later- 

 ally, and resemble free arm plates. Arm openings directed horizontally, ar- 

 ranged in groups of 4, 3, and 4 ; the interspaces between the arms of the same 

 ray narrow and slightly grooved, those between different rays much wider 

 and deeply depressed. Structure of arms unknown. Regular interbrachials 

 three ; the first large, about as wide as high and tuberculous, the two others, 

 which are on a level with the arm-bearing plates, small, elongate and flat. 

 Posterior interradius very wide ; it consists of a longitudinal row of three 

 anal plates, of which each succeeding plate is one half larger than that below, 

 and four interbrachials, two at each side of the anal series. The upper anal 

 plate supports a very conspicuous oval protuberance, which extends promi- 

 nently outward, and projects upward frequently beyond the central part 

 of the disk, giving to the calyx an asymmetrical aspect. Ventral disk 

 depressed hemispherical, crowned with five radial spines ; the posterior oral, 

 as in the preceding species, being merely convex or conical. The an-ange- 

 ment of the orals in this species is more symmetrical than iisual in this 

 genus, although the posterior one is not only larger than the others, but 

 pushed in slightly between them. The spines, which are comparatively 

 short, taper rapidly, and are succeeded toward the arms by two small second- 

 ary radial plates, and each of them by still smaller tertiary plates, which 

 enclose a small interambulacral. The anus opens out laterally, and occupies 

 the median part of the anal protuberance. 



Horizon and Locality. — Upper part of Upper Burlington limestone; 

 Burlington and Pleasant Grove, Iowa. 



Type in the Museum of Comparative ZoSlogy. 



Remarks. — This species differs from D. missouriensis in the more conical 

 ■ form of the dorsal cup, in its much narrower base, in the extravagant 

 development of its anal area, and in having an additional arm in all three 

 anterior rays ; all of which are constant characters. 



