FROM THE 



CARBONIFEROUS LIMESTONE OF IOWA. 597 



cavity, at the bottom of which is situated the basal plate; inferior edge very short, lateral edges straight; 

 superior angles obtuse : in their connexion they form a pentagon with straight or slightly concave edges. 

 Second series five, longer than wide, and more than double the size of those of the first series, smooth, 

 moderately convex ; three are pentagonal, and two irregular and hexagonal, resting by their edges on the 

 superior edges of the first series. Suj)erior plates pentagonal, short, width about double the length ; 

 inferior angles obtuse ; lateral edges straight, superior edges slightly concave ; facets for the arms nearly 

 equal to the entire width of the plates. Accessory pieces three, irregular, one oblong quadrangular, two 

 sub-pentagonal. The quadrangular plate is larger than the rest, and its superior angle is truncated to 

 support one of the smaller accessory pieces. A few joints of the arms are preserved in the only specimen 

 we have found of this species, viz. : a single brachial piece, which is pentagonal and slightly arcuated on 

 the lateral edges; on its oblique upper edges rests the commencement of a double series of hand joints, 

 consisting of wedge-shaped pieces. 



The column has not been discovered; judging, however, from the small impression on the calyx, it 

 must have been very slender in comparison with the size of the body. 



It occurs at Chester, Illinois, where it occupies a similar geological position to the preceding species. 



EXPLANATION OF FIGURES. 



Fig. 5. a. Side view, showing the form of the accessory pieces, and a few of the joints of the arms remaining at- 

 tached. 

 " b. Basal view. 



GENUS AGASSIZOCRINUS. (Troost in MS.) 



AGASSIZOCRINUS CONICUS. (N. S.) 

 (Tab. V. B, fig. 0.) 



Calyx. — Elongate-conical; plates massive; surface smooth ; internal cavity small. Column none. 



Basal plate conical, rounded at base, exhibiting no marks for the insertion of a column ; sides slightly 

 convex, consisting of five pieces, closely adhering among themselves, frequently anchyloscd ; length rather 

 more than half the entire height of the calyx ; superior edge with five slightly bevelled facets, on which 

 repose the first series of pieces. First series, five, pentagonal, thick, very slightly convex, length and 

 breadth about equal. Superior pieces five, pentagonal, wide, and very short; upper edges straight. 



Arms unknown. 



It occurs with Agassizocrinus dactyliformis and Pentrcmites jlorcalis, in the subcarboniferous lime- 

 stone at Chester, Illinois. 



STNBATHOCRINUS DENTATUS. (N. S.) 

 (Tab. V. b, fig. 7, a, b.) 



Calyx. — Conico-cupuliform ; plates massive; surface smooth; internal cavity small, occupying less 

 than half the diameter of the body ; arms five ; column round ; alimentary canal pentalobate. 



Based p>late saucer-shaped, pentagonal, tripartite; two of the pieces are wide pentagonal, and one has 

 the figure of a trapezium ; superior edges slightly concave ; impression for the column equal to about 

 half the diameter of the plate, circular, slightly excavated, striated on the margin ; central perforation 

 small, pentalobate. Superior plates five, sub-quadrangular, widest above ; upper edge straight or slightly 

 concave, furnished at their internal margins with two triangular tooth-like elevations, which form abut- 

 ments for the arms and prevent their displacement internally ; articular facets for the arms large, occupy- 

 ing the entire breadth of the plates. 



It occurs rather abundantly in the encrinital beds of the subcarboniferous limestone at Burlington, 

 Iowa. 



The basal plate of the genus jSynoathocrinus is described by Austin as being undivided. (Monograph. 

 Recent and Fossil Crinoidea, page 93.) We are convinced, however, from an examination of numerous 

 specimens from Kentucky, Indiana, Iowa, and Tennessee, that this is an error. In all well-preserved 

 specimens we have found the basal plate to consist of three pieces. 



