30 



portionally higher and the vault proportionally lower ant) so on, 

 but the species are so different from each other that they never, 

 even in fragments, can be mistaken for each other, and no light 

 would be thrown upon them by pursuing the comparison. And 

 so it will be found by comparing it with any other defined species. 



Found by Prof. A. G. Wetherby, in the Keokuk Group, in 

 Brown county, Kentucky, and now in the collection of Wm. F. E. 

 Gurley. 



AGARICOCRINUS ARCULA, n. sp. 



Plate III, Fig. 7, basal view of a large specimen; Fig. S, sum- 

 mit view of a small specimen; azygous view of the same. 



Species medium size and preserving all the characters ascribed 

 to it, in numerous specimens. Calyx deep, subcorneal; outline, sub- 

 pentagonal. All of the plates of the calyx are flattened or con- 

 cave, and conform to the outline of the calyx, none of them are 

 convex. 



Basals small, entirely hidden bv the column, that is, they form 

 a little cup which is filled by the column, while the first primary 

 radials rest upon the top of the cup. First primary radials rather 

 longer than wide, a small part abruptly bent into the columnar 

 concavity, three hexagonal, two heptagonal. Second primary 

 radials somewhat irregular in outline, quadrangular, and fully as 

 long as wide. Third primary radials larger than either the first 

 or second, three hexagonal, two pentagonal, axillary, and support 

 on each superior sloping side two secondary radials, which gives 

 to this species ten arms. The arms are composed of a double 

 series of short plates, from the commencement, united by the 

 usual zigzag suture. 



There are three plates in each regular interradial area. The 

 first is an elongated octagonal plate that rests between the supe- 

 rior sloping sides of the first primary radials and separates the 

 second and third primary radials and is followed by two narrow 

 elongated plates that separate, in part, the third primary radials, 

 and both secondary radials and unite with two plates belonging to 

 the vault. There are seven plates, in the azygous area. The first 

 one is in line with the first primary radials, but somewhat longer 

 * and narrower. It is followed by three plates, that separate the 

 primary and first secondary plates, and are of nearly the same 

 size. The third range consists of three plates, the middle one of 

 which is the widest, that separate the second secondary radials 

 and unite with the plates of the vault 



