PLATYCRINID^. 657 



tapering only near the ti]3s ; the two lower arm plates suturally connected 

 and quadrangular; the five or six succeeding ones wedge-form and uni- 

 serial, those beyond interlocking, and gradually turning into two series of 

 transverse pieces with parallel upper and lower faces. Pinnules heavy, 

 knife-like, the joints long and thickened at the ends. Ventral disk half the 

 height of the dorsal cup, flattened at the summit, the sides steep, almost in 

 a vertical line with the radials. The interambulacral spaces at the four regu- 

 lar sides generally consist of six pieces, arranged in two rows ; the middle 

 one of the lower row large, the two at the sides very little curving, the three 

 upper ones small. The interambulacrals of the anal side considerably wider, 

 the middle plate of the first row shorter and descending to a lower level than 

 the corresponding plates of the other sides, its lower faces making a right 

 angle ; the plates above numeroiis, forming a small protuberance, which 

 opens out laterally, and is separated from the orals by several moderately 

 large plates. 



Horizon, and Locality. — Lower Burlington limestone, Burlington, Iowa, 

 and Hannibal and Sedalia, Mo. 



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



Remarks. — This species resembles P. bwUngtonensis, but differs in the 

 more elongate form of the calyx ; it has no such anal tube as that species, 

 its anus consisting of a simple opening directly through the disk. 



Miller's P. carchesiimi, as described from the basals and radials only, can- 

 not be separated from P. jnleiformis. 



Platycrinus corbuliformis Rowley and Hake. 

 Plate LXXI. Figs. Ua, h. 



1891. Kansas City Scientist, p. 113, Plate 3, Figs. 1 and 3. 



Of the type of P. hurlingtonensis, but the plates heavier and more spread- 

 ing. Described from specimens in which only the basals, radials and a few 

 of the interradial plates are preserved. Dorsal cup basin-shaped, rather 

 rapidly spreading, and distinctly quinquelobate at the upper end ; the plates 

 convex and perfectly smooth ; interbasal, basi-radial and interradial suture 

 lines rather deeply depressed. 



Basals forming a shallow cup, with a deep circular depression at the 

 lower face for the reception of the column, which occupies about one third 

 the diameter of the cup ; the lower margins a little bulging, and curving 



