OWEN AND SHUMARD'S FOSSIL CRINOIDEA. 93 



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 attached. 

 " b. Basal view. 



Genus AGASSIZOCRINUS, {Troost in MS.) 



Agassizocrinus conicus. (New sp.) 



PI. XL fig. 6. 



Cahjx. — 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 anchylosed ; length rather more tlian 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 Pentremites Jlorealis in the 

 sub-carboniferous limestone at Chester, Illinois. 



Synbathocrinus dentatus. (New sp.) 

 PI. XI. 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. 



Basal plate 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 edges straight or slightly 

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

 which form abutments for the arms and prevent their displacement internally ; 

 articular facets for the arms large, occupying the entire breadth of the plates. 



It occurs rather abundantly in the encrinital beds of the sub-carboniferous limestone 



at Burlington, Iowa. 



24 



