LEPIDESTHES. 417 



plates in this fourth column, above which three columns continue to the dorsal limit of t he- 

 test (p. 374). A similar short-lived fourth column exists ventrally in other specimens of the 

 species where this area is clearly preserved (Plate 67, fig. 9). There are only three species 

 known in the Perischoechinoida which are characterized by three columns of plates in an 

 interambulacrum at the mid-zone (p. 221). These are: the present species, MeUmechinus 

 obovdtus sp. nov. (p. 374), and Meekechinus elegans sp. nov. (p. 444). The peristome, apical 

 disc, and periproct are not preserved in the known specimens of this species. The lantern is 

 inclined and pyramids are wide-angled, with a moderately deep foramen magnum. The 

 epiphyses are narrow, capping the half-pyramids (Plate 67, fig. 12). 



Keokuk Group, Lower Carboniferous, Crawfordsville, Indiana, F. Braun Collection, one 

 specimen; Museum of Comparative Zoology Collection, four specimens, nos. 3,057, 3,171, 

 3,172, and 3, 185; Yale Museum Collection, three specimens, nos. 318, 319, and 320; F. Springer 

 Collection, two specimens, no. 8,018. The holotype, which is in the Boston Society of Natu- 

 ral History Collection 11,601, was without an original label, but from the lithological character 

 and associated fossils, it is in all probability from Crawfordsville or that vicinity. 



The type as above noted is a small specimen (Plate 66, fig. 3; Plate 67, figs. 9, 12), not 

 much more than half grown. The ambulacral plates at the mid-zone are very nearly rhombic. 

 This is apparently an immature character as in the larger specimen (Plate 66, fig. 1), the plates 

 at the mid-zone are hexagonal, while the younger dorsal plates are more nearly rhombic 

 (p. 426) . In the type there are only four columns of ambulacral plates ventrally, as seen in 

 area B, and these are wider and lower than the more dorsal plates. There are three columns of 

 plates in an interambulacral area at the mid-zone and throughout most of the area, but there are 

 four columns of plates ventrally for a short distance in both areas A and C. This specimen on 

 the reverse side has a well preserved pyramid with an epiphysis in place on one side (Plate 

 67, fig. 12). This is all that is known of the lantern in this species. 



Mr. Braun's specimen (Plate 66, fig. 1 ; Plate 67, fig. 8) is the largest known in the species 

 and is beautifully preserved. The ambulacral plates are wide hexagons at the mid-zone with 

 pore-pairs set toward the next adjacent interambulacrum on either side. The interambulacral 

 plates show the imbrication well, and in area A, where some plates are absent, the beveled 

 edges are plainly seen. Ventrally, in area A are seen the introduction and dropping out of 

 column 4. 



The Museum of Comparative Zoology specimen, no. 3,171 (Plate 66, fig. 2; Plate 67, fig. 10), 

 is less nearly complete, but is beautifully preserved. Ambulacral plates at the mid-zone are 

 hexagonal, and the occluded plates are somewhat wider than those of other columns. The 

 pore-pairs are in peripodia and tubercles are very plain. 



Of the three Yale Museum specimens, one is very small, the youngest specimen of the 

 species seen. Another has the spines well preserved (Plate 67, figs. 13, 14) as described above. 



