16 



u;)on each upper side three secondary radials, which gives to 

 it two arms. There are. therefore, sixteen arms in this species. 

 The arm formula is 3+4+2+4+3. 



All of the interradial areas connect with the vault. There 

 are live plates in each of two reojular interradial areas, one in 

 the first range, two in the second, and two in the third, the longer 

 one of which unites with the plates of the vault. In each of 

 the other two regular interradial areas there are six plates, 

 one in the first range, two in the second and three in the 

 third, one of which connects with the vault in one area and 

 two in the other. In the intcrsecondary area, in the ray on 

 the right of the azygous area, there is a plate inserted that 

 connects with the plates of the vault. The azygous area is 

 subelliptical in outline, and contains fourteen plates. Th(> first 

 on3 is in line with the first primary radials and of about the 

 same size, it is followed by three plates in the second range, the 

 middle one of which is much the largest. There are five 

 plates in the third range, and an intercalated plate over the 

 last one, on the left side. There are two small elongated 

 plates in the fourth range by the side of the upper part of 

 the largest plate, in the third range, which gives us three 

 plates in width at this point, all of wliich \inite with two 

 elongated j^lates that unite with the plates of the vault. The 

 last two plates unite with a first tertiary radial on the left and 

 a second tertiary radial on thc^ i-ight and then (extend u]) ovei' 

 part of the vault. 



The vault is convex and covered with numerous convex, 

 polygonal plates and bears a subcentral proboscis. The inter- 

 radials are depressed toward the margin. 'Cliere is an ovarian 

 I^ore on each side of eacii ]>;iii- of arms and on c^ach side of 

 each single arm, which gives to tliis species eighteen ovarian 

 apertures. 



There has never been but four sixteen-armed species heretofore 

 described from the Burlington Group, and neither one of them 

 has any i-esemblance to this S])ecies. Tiiis species is, there- 

 fore, distinguished by its arm formula, general shape, and reg- 

 ular inlei'radial areas and azygous area. 



Found in the Burlington (ii'oup, at Burlinzlon. Iowa and 

 now iu the collection of Wm. F. E. Gurlcy. 



