21 



series of interlocking plates, at the base of the arms. There are, 

 tlierefore, eleven arms composed at their bases of a double series 

 of iuterlocking plates. 



The first interradials are the larger plates of the body and have 

 nine sides. Thej^ are deeply stellate in their ornamentation. The 

 second interradials are more than twice as wide as high and ap- 

 parently heptagonal as the two superior sloping sides of each ap- 

 pear to bear four small plates that separate the second and third 

 secondary radials. These plates are followed by two plates that 

 separate the fourth secondary radials, and upon the superior lateral 

 sides of these plates there is a single small plate, on the side of 

 the arm base, that appears to properly belong to the calyx. There 

 are, therefore, ten regular interradials if the last two small plates, 

 above mentioned are to be regarded as interradials. Tlie sutures; 

 between the intersecondary radials cannot be distinguished in ouF;-; 

 specimen, but, from the ornamentation, it is inferred there is one, 

 small plate in the first series and two in the second. No azygous 

 area has been determined. 



The vault is moderately and evenly convex, with very slightly 

 concave interradial spaces and a small, long subceutral proboscis. 

 It is covered with rather large polygonal plates, the ornamentation 

 of which is destroyed in our specimens. The plates in the inter- 

 radial areas are elongated and arranged in fan-like order. A hor-- 

 izontal furrow crosses the top of each of the last plates in the 

 calyx, except the minute ones abutting the arm bases, and pene- 

 trates the vault at tlie suture between tlie plates of the interradial 

 and intersecondary radial areas. Our specimens disclose four 

 of these horizontal elongated passages in each interradial area and . 

 two in each secondary interradial area. 



A glance at the vault of this species will at once distinguish it 

 from D. orwtius, D. ornaius car. asprrafits and all other de- 

 scribed species. Beside it is remarkable for the comparatively low 

 calyx, broad and deep basal concavity and dense stellate sculptur- 

 ing of the surface. 



Found in the Hamilton Group, at Louisville, Ky., and at Char- 

 leston, Indiana, and now in the collection of Wm. 'F. E. Gurley. 



