436 ROBERT TRACY JACKSON ON ECHINI. 



plate (Plate 73, figs. 3, 4; Plate 74, fig. 1). The lantern is inclined, teeth are grooved, and 

 pyramids wide-angled, with moderately deep foramen magnum (Plate 74, figs. 2, 6, 7). 



Keokuk Group, Lower Carboniferous, Hamilton, and near Nauvoo, Illinois; these are the 

 original localities given by Meek and Worthen. The type is said to be in the Worthen Col- 

 lection which is now in the University of Illinois, at Urbana, Illinois. Keokuk Group, Keokuk, 

 Iowa, F. Springer Collection 8,015, 8,017; Montgomery County, Indiana, F. Braun Collection, 

 two specimens; Warsaw, Illinois, Museum of Comparative Zoology Collection 3,070; Keokuk, 

 Iowa, two interambulacral plates, Museum of Comparative Zoology Collection 3,182; near 

 Burlington, Iowa, University of Michigan Collection 1,740. Lower Carboniferous, Omer, 

 Michigan, dissociated plates that I collected at that locality, Museum of Comparative Zoology 

 Collection. 



Up to the present, the best published figure of this species is that given by Meek and 

 Worthen (1873), here reproduced as Plate 75, fig. 3. As they had no genital plates, or other 

 structures to locate the axes, their figure was incorrectly oriented, which led to a wrong im- 

 pression as regards the direction of imbrication (p. 76). The orientation is corrected in my 

 Plate, and therefore shows the imbrication of interambulacral plates as aboral, which is correct. 

 In this figure in area A there are a left adradial and three median columns. The adradial plates 

 are very large and have the eccentric perforate primary tubercles, with numerous small second- 

 aries characteristic of this column dorsally. The median plates have secondary tubercles 

 only. All the plates are strongly curved outward and rounded on the suture lines as is typical 

 of the species. In ambulacrum B there are four small ambulacral plates, not in place, but 

 typical of the dorsal side. In addition, there is a quantity of small bodies, plates perhaps, 

 which are apparently foreign to the specimen, and are scattered indiscriminately in ambulacral 

 and interambulacral areas. Meek and Worthen's figure of the reverse side of the same speci- 

 men, reproduced as my Plate 75, fig. 4, shows a confused mass of plates from the ventral side. 

 The ambulacral plates are rounded in outline, and much larger than on the dorsal side. The 

 pore-pairs are about in the middle of each plate, and are surrounded by a sunken ring, and the 

 pores are on an elevated prominence, resembling the holes on the back of a button. The inter- 

 ambulacral plates are small, mostly with primary and secondary tubercles, and numerous 

 primary and secondary spines are scattered over the plates. A single primary spine restored, 

 and magnified "about twice," copied from Meek and Worthen (my Plate 75, fig. 5), shows the 

 form well; it is considerably larger than any spine of this species that I have seen. 



Mr. Braun's specimen, from Montgomery County, Indiana (Plate 75, fig. 2; Plate 73, 

 figs. 4, 5), is a small individual, but it is the most nearly complete dorsal view of any specimen 

 known. On account of the lightness and delicacy of the test of this specimen and the next 

 one described (Plate 75, fig. 1; Plate 73, fig. 3), my first impression was that it represented a 

 distinct species, but as the structural characters are the same as in large undoubted specimens 



