480 PALS ONTOLOGICAL REPORT OF GEOLOGICAL SURVEY. 



generally prominent tubercles, usually rounded and low, sometimes 

 long and sharp-pointed; an additional knob or point usually marks the 

 summit, which is sub-central and near the anal side; around these 

 prominent pieces, are arranged, in a circular manner, small polygonal 

 pieces of various sizes, and the interspaces between these circular 

 patches are filled with pieces . of irregular forms; in some of the 

 best preserved several knobs are joined by the interspace, having s 

 central piece, around which are arranged, circularly, small pieces-— -one 

 piece of the circle forming the connection between the centers of the 

 adjoining circles. 



Oar description is that of a single specimen, differing in many par- 

 ticulars from all others of the species; yet it is believed that no accu- 

 rate observer could fail to reorganize every specimen of the species, 

 by features they have in common, which distinguishes them from oth- 

 er species. 



Basal pieces. The basal pieces, when undivided, presents an oblong 

 hexagonal space — the middle perforation being sub-central; when di- 

 vided, the sutures from the central opening terminate at the center of 

 the inferior margin of the alternate radial pieces of the first series; by 

 this division producing two pieces nearly equal in size, and one gene- 

 rally smaller than the others. 



Radial pieces, 1 st series. Consists of six hexagonal pieces, (one of 

 these pieces is sometimes pentagonal or obscurely hexagonal,) differing 

 somewhat in size and form ; slightly concave — the concavity extending 

 over the whole area of each piece; when arranged in the cup they are 

 nearly horizontal, being only slightly curved. 



Primary radials, 2nd series, five; usually four hexagonal and one 

 pentagonal ; not unfrequently one of the radials is abnormal, and rises 

 between two of the radials of the first series. Fig. lb, plate IV, ex- 

 hibits this anomalous arrangement. Fig. la, plate IV, shows all the 

 pieces in a normal condition (hexagonal.) 



The 3rd series of primary radials consist of four pieces septilate- 

 ral, and one hexagonal ; nearly equal in size. 



Secondary radials, 1st series, consists of eleven pieces, varying in 

 size and form — some being heptagonal, hexagonal, and one being pent- 

 agonal; this last piece rises from the anomalous ray. (Fig. lb, plate 

 IV.) 



