26 



becomes obsolete toward the center. The capacity of the vault 

 is less than that of the shallow calyx. The vault bears a 

 rather large, convex, central plate and is otherwise covered 

 with small and less convex polygonal plates. The Large tumid 

 plates that usually extend from the arms to the summit in this 

 genus, do not characterize this species. The azygous orifice is 

 not elevated or situated on a tumid swelling, as is usual in 

 this genus, but is surrounded by small plates and a short side 

 of the large central plate. 



The depressed, short body, pentagonal outline of the calyx, 

 small plates of the vault, single interradials, four azygous 

 plates and ten arms are features that distinguish this species 

 from all others. There is no described species, from the Bur- 

 lington Group, with which it can be said to have much re- 

 semblance, but in its short body and general form it partakes 

 of the character of A. blairi, from the Chouteau limestone. 

 though the latter has only nine arms, is subquadrate in out- 

 line, and has more plates in the azygous and regular areas 

 than this species has. It cannot be mistaken for any other 

 described species. 



Pound by C. S. Hodgson, in the Burlington Group, in Adams 

 county, Illinois, and now in the collection of S. A. Miller. 



AMPHORACHIM S BLAIRI, 11. sp. 



Plate I, Fig. 45, basal view; Fig. 46, same magnified tiro diameters; 

 Fig. 47, summit view; Fig. 48, same magnified tiro diameters: 

 • Fig. 49, azygous side; Fig, 50, same magnified tiro diam- 

 eters. It will he observed thai one of the rays ad- 

 joining the azygous area is injured, so it 

 is not shown in the illustrations. 



Species very small. Calyx broadly rounded below, bowl 

 shaped, or somewhat hemispherical. About twice as wide as 

 high. Surface of test granular. No radial cidges. 



I!:isals form an hexagonal disc one half wider than the 

 diameter of the column. First primary radials about as long 

 :is wide, three hexagonal, two ueptagonal. Second primary 

 radials smaller than the first, a little wider than Long, hexag 

 onal. Third primary radials somewhal smaller than tin- sec- 

 ond, pentagonal, axillary and support on each upper sloping 

 side a single secondary radial, which gives to each ray two 

 arm openings to the vault, There are. therefore, ten arms in 



this species. The secondary radials are directed horizontally 



