BATOCRINID#. 467 
Fforizon and Locality. —In the lower part of the Upper Burlington lime- 
stone, not found above the white crystalline bed, Burlington, Iowa. 
Type in the Illinois State collection, Springfield. 
Dorycrinus unispinus (Ha11). 
Plate XLV., Fig. 12. 
1861. Actinocrinus unispinus—Hati; Prelim. Desc. New Crinoids, p. 2, and Bost. Journ. Nat. Hist. 
p- 270. 
1873. Dorycrinus unispinus —MxEEK and WortHEN; Geol. Rep. Illinois, Vol. V., p. 380. 
1881. Dorycrinus unispinus — W. and Spv.; Revision Paleoer., Part IL., p. 180. 
Syn. Actinocrinus trinodus Watt; 1858, Geol. Rep. Iowa, Vol. L., Part II., p. 575. 
Calyx moderately spreading to the top of the second costals, and thence 
more abruptly to the arms; it is distinctly truncated at the base, and, as 
seen from above or below, somewhat pentalobate at the arm regions. Ven- 
tral disk depressed convex, one fourth to one third shorter than the dorsal 
cup, and crowned by a single large spine. The plates of both hemispheres 
are not ornamented; they are virtually flat, with only the apparent convex- 
ity due to the slight grooving of the suture lines. 
Basals forming a short cup, subcylindrical in outline, often slightly 
spreading to the lower margin, excavated at the bottom enough to enclose 
the two proximal stem joints, and pierced by a small pentangular canal. 
Radials a little wider than long, as large as the two costals together, the 
upper face concave. First costals quadrangular, nearly twice as wide as 
long, upper and lower faces convex. Second costals a little wider and 
longer. Number of arms exceedingly variable, with consequent variation 
in the distribution of the distichals and the presence or absence of palmars. 
The anterior and two posterior rays have either three or four pairs of arms; 
in the latter case there is but one distichal in both divisions, succeeded by 
2X 2 palmars, but if there are three pairs, the two divisions next the anal 
interradius have no palmars.’ The two antero-lateral rays rarely have more 
than two pairs of arms, and 2 X 2 distichals. Arm openings directed out- 
ward, arranged in groups; those of the same ray separated from those of 
adjoming rays by adeep depression. Arms incurving, rather stout for the 
genus, flattened in their upper parts and serrated at the edges, but without 
increasing materially in width. Regular interbrachials three, rarely four, 
the upper row on a level with the arm bases. Posterior interradius wider, 
formed at the upper end into a longitudinal ridge with a deep groove at 
