BATOCRINID^. 509 



A very different species from A. ixntagonus, to wliich it has been referred 

 by Hall, in some respects approaching Am^ihoracrinus. Calyx pentalobate, 

 indented between the rays. Dorsal cup depressed saucer-shaped ; the ven- 

 tral disk irregularly hemispheric, bulging at the posterior side. The plates 

 of the former flat, the radials and first interbrachials sometimes a little con- 

 cave ; those of the tegmen more or less tumid ; suture lines distinct but not 

 actually grooved. 



Basals hidden by the column. Radials large for the genus, as long as 

 wide; their lower margins deflected to form the column concavity. First 

 costals quadrangular, once and a half as wide as long ; wider above than 

 below ; three of its faces convex, the upper straight. Second costals not 

 longer than the first but wider, the upper angle quite obtuse. Distichals 

 two, short and wide ; the upper one cuneate and followed by two rows of 

 alternately arranged arm plates. Arms two to the ray, not quite as heavy as 

 in some of the preceding species ; gradually tapering. First interbrachials 

 very large, rising to the first distichals ; width and length as three to four. 

 They are followed by two elongate plates, and these by a moderately large 

 number of interambulacral pieces. Anal side very wide. The first anal 

 longer than the radials, but not as wide ; supporting three plates, which are 

 remarkable for their width, being almost as wide as long. The next row 

 consists of four to five small pieces, which support in the disk numerous 

 others of irregular form. The pentamerous symmetry of the ventral disk is 

 considerably disturbed by the large anal area, which bulges conspicuously 

 from above the arm regions to the posterior oral ; it is, however, unlike that 

 of A. hellatrema, being composed of almost flat pieces, and bordered by 

 a shallow groove at each side. Anal opening directed obliquely upwards. 

 Posterior oral excentric, being pushed over to the anterior side ; it is as 

 large as three of the others together, and strongly nodose, while the others 

 are but little convex. The radial dome plates, if represented at all, were 

 small, not much larger than the interambulacrals, which in this species are 

 quite numerous. 



Horizon and Locality. — Upper Burlington limestone; Burlington, Iowa. 



Remarks. — Hall described this species as a variety of Agaricocrinus pen- 

 tarjonus as follows : " Base convex ; arms small ; all the plates of the dome 

 tuberculous." Not only is this description insufficient, but it is partly incor- 

 rect; the plates of the tegmen being convex but not tuberculous. The pres- 

 ent description was made from a specimen in the collection of Wachsmuth 

 and Springer. 



