PLATE 17. 



Lepidocidaris squamosa Meek and Worthen. Page 282. 



Figs. 1-14. Lower Burlington Limestone, Lower Carboniferous, Burlington, Iowa. 

 Figs. 1-5. Mus. Comp. Zool. Coll., 3,026. Same specimen as photograph, Plate 16, fig. 1. Holotype. 



Fig. 1. X 0.9. Eight columns of interambulacral plates in area A, the seventh and eighth columns coming in below the 

 mid-zone. 



Fig. 2. Ambulacral detail from the area marked X in fig. 1. X 3.7. Every third ambulacral plate is wider and higher 

 than the intermediate plates. 



Fig. 3. Ambulacral detail from area marked XX in fig. 1, from nearer the mid-zone than is fig. 2. X 3.7. Every third 

 plate higher and wider than the intermediate plates. In cases, some intermediate plates may be demi- or occluded 

 instead of all plates being primaries. (Compare fig. 7.) Primary tubercles of interambulacral plate perforate, with 

 wide scrobicule, but no basal terrace. 



Fig. 4. Plates from the upper part of ambulacral area B to show beveling dorsally, and laterally under the interambula- 

 crum. X 3.7. 



Fig. 5. Dental pyramid. X 2. Epiphysis wanting; corrugations present for the attachment of the interpyramidal 

 muscle. 



Fig. 6. Mus. Comp. Zool. Coll., 3,046. X 2. Dental pyramid, face view, foramen magnum moderately deep; the sutural 

 face for the epiphysis occurs on the left . 



Fig. 7. F. Springer Coll., 8,096; same specimen as photograph, Plate 16, fig. 2. X 1.9. Every third ambulacral plate 

 higher, wider, and apposed to two plates of the opposite half-area. Adradial plates are much narrower than inter- 

 ambulacral plates of the median columns. 



Fig. 8. Same specimen. X 7. Detail of typical ambulacral plates. A relatively high plate in one half-area is opposed 

 to two lower plates of the opposite half-area. 



Fig. 9. F. Springer Coll., 8,074. X 3.7. Interambulacrum with six columns of plates. There are four columns ven- 

 trally, the fifth and sixth columns coming in higher up. Ventrally there are some ambulacral plates which are evi- 

 dently peristomal and in the middle line the tip of a tooth in place. 



Fig. 10. Same specimen as fig. 7. X 3.7. Details of interambulacral plates with primary and secondary spines in place. 

 There is no basal terrace around the primary tubercles; the lines in the figure that might be taken to indicate that 

 structure are intended to represent the elevation of the boss. 



Fig. 11. F. Springer Coll., 8,095. X 1.8. Six columns of plates in two interambulacral areas, adambulacral plates are 

 narrower, primary spines in place. 



Fig. 12. Same specimen as fig. 7. showing the character of ambulacral and interambulacral plates and the bases of primary 

 spines. X 3.7. 



Fig. 13. Mus. Comp. Zool. Coll., 3,046. X 1.9. Complete primary spines. 



Fig. 14. F. Springer Coll., 8,096. Same specimen as fig. 7. X 3.6. Primary and secondary spines, showing their cylin- 

 drical character and fine vertical striae. 



