LEPIDESTHES. 427 



as in areas 1, 2, 3, and 5 of Plate 71, fig. 1; but sometimes the plates of column 4 are the wider 

 and imbricate laterally in two directions, as in area 4 of this same figure. In a total of 27 

 interambulacral areas observed, column 3 has the wide plates in eighteen cases and column 4 

 has the wide plates in nine cases. Why there is this tendency to left-handedness in regard 

 to which column has the wide plates, is without explanation, but it emphasizes the definite- 

 ness of arrangement in trifling details. The interambulacral plates as seen from the interior 

 are angular, and imbricate adorally and from the sides toward the center; also the ambulacral 

 plates in this view bevel over the ambulacrals. This relation of imbrication seen from the 

 exterior and interior is shown diagrammatically in text-figs. 32 to 38, p. 75. Interambulacral 

 plates, like the ambulacrals, bear small secondary tubercles and spines about 1.8 mm. in length. 



The plates of the peristome are not preserved in any of the specimens, but tips of the 

 dental pyramids and teeth are in place in two cases. The apical disc is in place in two speci- 

 mens (Plate 69, figs. 1, 5; Plate 71, fig. 1; text-fig. 251). In the larger of these specimens 

 (Plate 69, fig. 1) the apical disc measures about 6 mm. in diameter and the specimen about 

 37 mm. in diameter. The apical disc is therefore relatively small, being proportionately about 

 16 % of the diameter of the test. A small apical disc is a progressive character (p. 87) and is 

 in keeping with the great development of the ambulacrum which marks this species as a highly 

 specialized type amongst Echini. The oculars are rounded plates, lying above the ambulacral 

 areas and covering the interambulacra in part on either side, seen clearest in areas I and V 

 (text-fig. 251). The genitals are wide, rounded plates. Genital 1, which is partially hidden, 

 shows two pores, and genital 5 has three pores. Genital 2 shows numerous clear, fine madre- 

 poric pores, and by this structure the specimen was oriented by the Loven method. Rather 

 curiously the madreporite does not show any genital pores. Genitals 3 and 4 are in part 

 hidden and do not show any pores. The plates of the periproct are numerous, small, rounded, 

 similar to those oi Lepidesthes formosa (pp. 413, 419). 



Keokuk Group, Lower Carboniferous, Salem, Washington County, Indiana. This is the 

 locality of Dr. White's holotype, the only one he had when first publishing the species. I do 

 not know where the specimen is; the specimen from the same locality, of which he published 

 a figure in his second paper on this species (1880a), is in the University of Chicago Collection 

 6,340. The location of the specimen which Dr. Wliite figured in his third paper (1882) I do 

 not know. The same horizon, Bono, Indiana, University of Chicago Collection 6,641 ; Bono, 

 Lawrence County, Indiana, two fine specimens. Museum of Comparative Zoology Collection 

 3,183, 3,184; Montgomery County, Indiana, Museum of Comparative Zoology Collection 

 3,176, 3,177, 3,178, and 3,179; British Museum Collection E 10,677; F. Braun Collection, 

 two specimens; Indian Creek, Montgomery County, Indiana, F. Springer Collection 8,102. 



The specimen figured by Dr. White (1880a), as stated, is in the University of Chicago 

 Collection. As it is not the original single specimen he had when he first published the species, 



