12 



Basals form an hexagonal disc more than one-half wider than 

 the diameter of the column. First primary radials very large, 

 about as liigh as wide, three hexagonal, two heptagonal. Sec- 

 ond primary radials quadrangular, from three to four times as 

 wide as long. Third primary radials a little larger than the 

 second, about three times as wide as long, pentagonal, axillary, 

 and in three of the rays bear upon each upper sloping side two 

 secondary radials, which gives to each of these rays two arms. 

 In each ray adjoining the azygous area tliere are two sec^ond- 

 ary radials on the distal side of the third primary radial and 

 two on the proximal side, the last being axillary, which gives 

 to each of these two rays three arms. There are, therefore, 

 twelve arms in this species. The arms are very strong and, 

 above the first two or three cuneiform plates, are con^josed of 

 a double series of interlocking plates as is usual in this genus 

 The arms are subfusiform and slightly flattened at the superior 

 ends. 



There is one plate in each of the regular interradial areas. 

 The first azygous plate is in line with the first primary radials 

 and the largest plate in the body. It is followed by three plates 

 in the second range which separate the .secondary radials and 

 unite with three plates belonging to tlie vault. 



The vault is coiioidal. Proboscis not oxpo.sed in our speci- 

 men. 



This is tlic second species ever desci-ibtnl from tlie Keok-ulc 

 Group having twelve arms. The other is B. intrgravis, to 

 which this one has no I'esemblance. This species is distin- 

 guished by its general form, twelve arms and wide azygous 

 area and cannot be mistaken for any other. 



Pound in the Keokuk Group, at Boonville, Missouri, and 

 now in tlie collection of Wni. F. K. (Iiirley. 



1!.\T()('UI.\TS DKl.KW'ITl.rS, \\. S]). 



Plate 1, Fiji- 20, (izijiious side of (i specimen somewhal compressed 



magnijied two iliomelers : fin- ~I, oppoiite side view 



of same magnified ixco diameters. 



Species very small and delicate, somewhat biturbinate. Calyx 



obpyramidal, twice as wide as high. Plates convex, more or 



less angular. Radial ridges well defined, interradials depi-essed, 



and all the interradial areas connect with the vault. 



