NATURAL SCIENCES OF PHILADELPHIA. 79 



nearly in their relative positions, excepting that they are all spread almost on 

 a plane, and more or less displaced and broken by accidental pressure. Here, 

 near the ends of the areas, there are apparently only two rows of interambu- 

 lacral plates in each series, the two ranges measuring together only about 0-40 

 inch in breadth ; soon, however, they pass into three or four ranges. The am- 

 bulacral areas, at about one inch from the apparent position of the oral orifice, 

 measure nearly an inch in breadth, and, as near as can be counted, there appear 

 to be there six or more ranges of ambulacral plates. These plates appear to 

 increase in size and decrease in number toward the end of the areas, so that 

 some of them are there nearly as large as the adjacent interambulacral plates. 

 They are generally wider than long, and as they lie together present more or 

 less rhombic faces, arranged somewhat like the scars on the surface of some 

 species of Lepidodendron. This similarity is also increased by the pores, and 

 some little pits in the central region, surrounded by the circular depression. 

 Some of the larger of these plates have the pores near one end, and a tubercle 

 occupying the middle, nearly as large as the primary tubercles on the adjacent 

 interradials. These probably belong to the middle ranges. 



The larger primary spines attained a length of about one inch, and a thick- 

 ness of 0-10 inch at the head, which is a little swollen; above this they taper 

 rather gradually, are rounded, nearly straight, and marked by minute, crowded, 

 longitudinal striae. Among the ambulacral plates there are also seen lying 

 scattered about a number of other spines, from one-fourth to one third the 

 size of those described, and of very nearly the same form. These seem to be- 

 long to the ambulacral plates, on most of which we see a tubercle larger than 

 the secondary tubercles of the interambulacral plates. Many much smaller 

 spines than the latter are likewise seen, that probably belong to the secondary, 

 or perhaps, more properly, tertiary series. 



Locality and position. Hamilton and near Nauvoo, Illinois ; in the Keokuk 

 division of the Lower Carboniferous Series. 



EociDAUis? SQUAMOSA, M. and W. 

 Body attaining a large size, apparently depressed-subglobose in general 

 form. Interambulacral plates rather thick, in eight or more longitudinal rows 

 near the middle of each area,* but apparently only the two outer rows con- 

 tinued to the oral aperture; all presenting the usual hexagonal form, except- 

 ing the pentagonal marginal rows, and distinctly imbricating apparently from 

 the lower side upward, f 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 ambulacral 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 distinctly 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, prominent, perfo- 

 rated, central process, for the immediate articulation of the primary spines; 

 most convex part of each plate surrounding the smooth, saucer-shaped depres- 



* Eight rows are seen in the specimen at the widest part, but we are not sure this is the 

 middle of the a^ea, owing to the imperfection of the specimen. 



t 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 

 fossil. 



1869.] 



