BATOCEINID^. 459 



majority of specimens only to the right ; while the antero-lateral rays have 

 two successive distichals and no palmars. Distichals and palmars are dis- 

 tinctly rounded off at the sides, lilie free arm plates. Arm facets semi-ovate ; 

 the ambulacral openings directed slightly upwards, arranged in groups of 

 four, two, and three (sometimes four in the anterior ray). The interspaces 

 between the rays are wide, abruptly and deeply depressed, especially at the 

 anal side, and those between the various ray divisions are deeply notched. 

 Arms in pairs, two from each arm opening, long for the genus, incurving, flat- 

 tened at the upper end, and every fourth plate giving off laterally from oppo- 

 site sides sharp spines, 2 cm. in length. Interbrachials three, i-ather large, 

 the two of the second row on a level with the arm bases. Anal area very 

 wide, forming a low elongate ridge, grooved along the sides, which extends 

 up to the posterior oral and contains the anus. First anal plate as long as 

 wide, followed by two other anals of smaller size, the two latter sustaining 

 an interbrachial at each side. Ventral disk hemispherical, with six long, 

 slender, sharply pointed spines. The posterior oral, or plate bearing the 

 middle spine, large and central, the other orals rather small and pushed 

 anteriorly. The five radial spines are followed by two small secondary 

 radial plates, and in rays with four arms by tertiary ones, whicli enclose 

 an interdistichal. Anus opening out laterally, placed at midway between 

 the posterior oral and the arm regions. Column very gradually sloping 

 downward, with small cirri at the lower end, one to a joint, and at irregular 

 intervals. The nodal joints of the upper portion of the stem are longer and 

 considerably wider than those of the lower end ; they project conspicuously 

 over the internodal pieces, but gradually decrease in length and width, and 

 at 5J cm. from the calyx have the same form and size as the others. The 

 last two internodes in one of the specimens both contain seven joints. 



Horizon and Locality. — Upper and Lower Burlington limestone, Burling- 

 ton, Iowa. 



Type in the (Worthen) Illinois State collection, Springfield. 



Remarks. — There can be no doubt that Actinocrinus diiwicafiis and 

 A. decornis, both described by Hall, and afterwards placed by us under 

 Dorycrinus, are mere variations of this species, as may be seen by com- 

 paring a large number of specimens. The former is a very mature form, 

 in which the anterior ray obtained an additional pair of arms ; in the latter, 

 which came from the Loiuer Burlington bed, one or both posterior rays have 

 but three arm openings, and, as a rule, the spines are shorter. The type 



