11 



primary vadials one half larger than the second, more than 

 twice as wide as long, pentagonal, axillary, and in the ray on 

 the left of the azygous area, and in each lateral ray, bear 

 upon each superior sloping side two secondary radials, the last 

 ones of which are axillary and support on each upper side 

 two tertiary radials, which gives to each of these rays four 

 arms. In the ray on the right of the azygous area there ai"e 

 three secondary radials on the distal side, and two t)n the 

 proximal side, the last one being axillai'y and supporting on 

 one upper side a single tertiary radial and on the other two 

 tertiary radials, which gives to this ray three arms. In the 

 ray opposite the azygous area, the third primary radial bears 

 upon each upper side three secondary radials which gives to 

 this ray*two arms. There are, therefore, seventeen arms and 

 seventeen ambulacral openings to the vault in this species. 



All of the interradial areas connect with the vault and are 

 depressed between the rays. In each regular interradial area 

 there are four jjlates. The first one is large, it is followed by 

 two plates, in the second range, and by one elongated plate, 

 in the third range, that unites with the plates of the vault. 

 In the azygous area there are eleven plates. The first one is 

 in line with the first primary radials and about as large. It 

 is followed by three plates in the second range, three in the 

 third range, two in th(T foui-th range, and two in the fifth 

 range tliat unite with the plates of the vault. 



Vault conoidal and covered with small, polygonal, convex 

 plates and bearing a very small subccntral i)rol5oscis. No 

 ovarian pores have been detected. 



This is a marked species so different from all other seven- 

 teen-armed species that occur in rocks of the same age that 

 no comjiarison with any of them is necessary. 



Found liy N. K. Burkett in the Keokuk Group, at Keokuk. 

 Iowa, ami now iu the collection of Wm. P. K. (Turlev. 



15.\T()('RlNrS KTliKNt'US, n. sp. 



Phile I. Fig. IS. nzi/iious side; Fiij. 19. side riew. 

 Si)('ci(\s siii;ill liut ln'uriug l;irg<' and vigorous ai'ms, l)iturl)in- 

 alc Calyx bo\vl-sha])ed, al)out twice as wide as high. NO 

 i-a(li;il ridiz:(»s. Plates convex. 



