PALEONTOLOGY OF IOWA. 689 



Dicliocrinus protubcrans ( n. s.). . 



PLATE XXV. FIG. 7. 



BODY depressed, twice as wide as high : base flat, with a 

 small central depression ; the two plates forming a pentagonal 

 disc, with a triangular indentation at the junction on one 

 side for the base of a long narrow anal plate. Radial plates 

 short, much wider than long, projecting below and laterally 

 beyond the plane of the basal plates in round tuberculiform 

 protuberances. 



( Structure above the radial plates undetermined.) 



This species, though so unlike the ordinary forms of Dichocrinus which have been 

 illustrated, I can refer to no other genus, since the division of the base is into two 

 parts. 



Fig. 7. View of the base, which shows the two basal plates, three of the protuberant 

 radials, and the narrow anal plate. 



Geological formation and locality. In the Kaskaskia limestone : Chester, 

 Illinois. 



GENUS ACROCRINUS (YANDELL). 



GENERIC DESCRIPTION. " Body goblet-shaped, constituted of 

 about sixteen series of plates [ which are ] generally hexa- 

 gonal, and increasing in size from the base to the summit ; 

 each series including from twenty to twenty-five pieces, the 

 last supporting five large arm-bearing plates, which give 

 origin to twenty rays composed of a double row of tentacu- 

 lated joints. Pelvis undivided? large, circular, saucer-shaped. 

 Column round, consisting of thin serrated joints, gradually 

 expanding towards the base of the cup." 



The specimen under consideration does not enable us to add much to the generic 

 description given, except that the ring-like pelvis presents a well-marked suture on 

 one side, so that the divisions have probably been two or three. 



[ IOWA SURVEY.] 87 



