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 arrange- 
ment of the orals in this species is more symmetrical than usual 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. 3 
Type in the Museum of Comparative Zodlogy. 
Lemarks, — 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. 
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