FOSSILS OF THE BURLINGTON GROUP. 479 



distinctly imbricating apparently from the lower side up- 

 ward.* as well as inward toward the central row. excepting 

 the two outer rows on each side, the lateral imbrication of 

 which is outward that is, the outer row laps the edge of 

 the ambulaeral series, and the next range laps the edge of 

 the outer row, while its inner edge laps that of the next 

 row within, and so on to the middle row, which is lapped 

 on both sides; each with a comparatively large, smooth, 

 saucer-shaped depression, occupying the central region, from 

 the edges of which the surface is distinctly beveled off in 

 every direction to the margins, the beveled edges that pass 

 under the edges of the adjacent plates, however, being dis- 

 tinctly wider than those lapping the adjacent pieces, these 

 lapping edges being as if ground off obliquely under, or, in 

 other words, beveled on the inner side ; tubercles for the 

 support of the primary spines smooth, prominent, rather 

 large, and rising in the middle of the saucer-shaped central 

 depression, narrowing upward to near the top, where there 

 is a circular depression surrounding a very narrow, prom- 

 inent, perforated, central process for the immediate articu- 

 lation of the primary spines; most convex part of each plate 

 surrounding the smooth, saucer-shaped depression, orna- 

 mented with a few very small pustules, upon which small 

 M rondary spines probably articulated. Primary spines ap- 

 parently one inch or more in length, rounded, slender, and 

 nearly or quite straight, with the articulating end perforated 

 and a little enlarged, so as to form an undefined ring. Sur- 

 face ornamented with minute, crowded, longitudinal stria?, 

 only visible by the aid of a good magnifier. Ambulacra 

 narrow, or nearly about equaling the breadth of the mar- 

 ginal rows of interainbulacral plates on each side, slightly 

 convex. Ambulaeral pieces slightly imbricating in the op- 

 posite direction from the interambulacral series, of very 



* This imbricating character, as well as several others mentioned in the above description, may be 

 of more than specific value, and they are mentioned here along with specific characters because we 

 are in doubt in regard to the generic relations of the fossils. 



