FOSSILS OF THE KEOKUK GROUP. 513 



placed and broken by accidental pressure. Here, near the ends of the 

 areas, there are apparently only two rows of interambulacral plates in 

 each >-..-rk-s. the two ranges measuring together only about 0.40 inch in 

 breadth ; soon, however, they pass into three or four ranges. The ani- 

 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 tie counted, 

 there appear to be there six or more ranges of ambulaeral pla 

 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 iuterambulacral plates. They are generally wider than 

 long, and as they lie together present more or less rhombic faces, ar- 

 ranged somewhat like the scars on the surface of some species of Lepi- 

 (loilf-ixlron. 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 iuterradials. These probably belong to the middle 

 rang 



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

 thickness 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 belong to the ambulacral plates, on most 

 of which we see a tubercle larger than the secondary tubercles of the 

 iuterambulacral 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 Xauvoo, Illinois; in the 

 Keokuk division of the Lower Carboniferous series. 



GEXTJS AGELACRIXITES, Yanuxem. 

 AGELACRIXITES (LEPIDODISCUS) SQUAMOSUS, M. and W. 



PL 16, Fie 1. 



Agelacriniie* (Lepidodigcuf) sqvamorus, MEEK and WOKTHKX. Proceed. Acad. Xat. Sci., Phila., 1868, 

 p. 357. 



DEPRESSED discoidal, outline circular, or somewhat oval. 

 Rays slender, long, and strongly curved as they radiate 



