OF ARTS AND SCIENCES. 23 



Basal pieces two, of tlie same form and size, prominent ; a broad, 

 shallow, elliptical depression surrounds the column : columnar pit small 

 and shallow, the line marking the junction of the pieces straight. 



Radial pieces five, obscurely hexagonal, about as bi'oad as high, 

 rising suddenly from the lines marking the lateral margins of the 

 pieces ; the upper corners truncated, thus forming an angular depres- 

 sion between the pieces for the reception of the inter-radial pieces. 



The second radials appear to have been quite small, and to have 

 stood prominently forward upon the summit of the first radial pieces ; 

 the facets by which they were attached to the first radials are all 

 that remains of them ; further their form and arrangement are un- 

 known. 



Inter-radials. The inter-radials are quite small, lozenge-shaped ; 

 they each support two interbrachial pieces of similar form. 



Anal pieces. The first anal piece rests in the deepest angular 

 notch in the basis, rising considerably higher than the first radials ; 

 like them it is hexagonal ; upon it rests a small hexagonal piece ; 

 this in turn supports upon its upper margin a pentagonal piece, the 

 upper part of which is elongated, and reaches to the oral (?) opening. 

 Between the first and second anal pieces, also between the second and 

 last piece described, rests, on either side, one small, lozenge-shaped 

 piece, the lowest forming one side of the circle about the arm open- 

 ings, the upper pair supporting small, pointed pieces lying above the 

 arms on either side of the anal field. 



Summit. The summit is covered by numerous small pieces, as in 

 D. symmetricus. A spinigerous piece rises in each group above the 

 arms ; the pieces surrounding the mouth are quite small, angular, the 

 apex of the angle toward the oral opening; they are about six in 

 number, and form a slight elevation upon the otherwise plane summit, 

 the oral opening being above the general level of the top of the vault, 

 the level part being covered by about ten polymorphous pieces. The 

 condition of our specimen is such that the arrangement of the pieces 

 surrounding the arm orifices cannot be satisfactorily made out; the 

 pieces appear to be more numerous than in D. symmetricus, and the 

 arms seem to have come off" from the body in sets of four ; making 

 twenty arms at the body. 



Arms. The form of the arms unknown. 

 Column. Unknown. 



