428 



ROBERT TRACY JACKSON ON ECHINI. 



it is not the type. It is a small individual (Plate 69, figs. 2, 3), about half grown, and is quite 

 typical in form, but somewhat flattened laterally. The ambulacral plates at the mid-zone 

 and throughout the areas are rhombic, as figured by Dr. White, not yet having taken on any 

 of the dorsal and ventral truncation of the plates seen in older specimens. A second speci- 

 men in the University of Chicago Collection is from another locality (Plate 69, fig. 4). This 

 is a larger individual, more nearly complete and perfect in form excepting for a little lateral 

 flattening. The ambulacral plates at the mid-zone (Plate 70, fig. 2), instead of being rhombic, 



IV. 



a 



TEXT-FIG. 251. Lepidesthes colletti White. Keokuk Group, Lower Carboniferous, Montgomery County, Indiana. 

 Museum of Comparative Zoology Collection 3,178 (from R. T. J. Coll.). Same specimen as Plate 69, fig. 1; Plate 78, 

 fig. 1. Ambulacra are dorsally simple. Oculars and genitals are broad, low, rounded; madreporic pores in genital 2. 



are narrow hexagons, having a short dorsal and ventral straight edge, but are not nearly so 

 wide as in those of a large individual (Plate 70, fig. 3). In the interambulacra of this specimen 

 (Plate 69, fig. 4) the plates of column 4 are wide in area A, but in area C the wide plates are 

 in column 3. 



A fine specimen in the Museum of Comparative Zoology shows a dorsal view somewhat 

 compressed, with a side thrust, but all the plates are in place (Plate 69, fig. 1; Plate 71, fig. !; 

 text-fig. 251). The ambulacral plates are rhombic, with 16 columns in each area at the mid-zone. 



